Add migrateNode20.md docs (#20181)

* Add migrateNode20.md docs

* explain why you need to specify minimumAgentVersion

Author: rumyax

docs/migrateNode20.md

@@ -0,0 +1,153 @@
+## Table of content
+
+[Update `typescript`](#update-typescript)
+
+[Update `@types/node`](#update-typesnode)
+
+[Update `task-lib` and `tool-lib`](#update-task-lib-and-tool-lib)
+
+[Add `Node20_1` handler](#add-node20_1-handler)
+
+[Specify `minimumAgentVersion`](#specify-minimumagentversion)
+
+[Test the changes](#test-the-changes)
+
+[Feedback](#feedback)
+
+## Update `typescript`
+
+Update `typescript` to the `5.1.6` version in `devDependencies` in the `package.json` file and fix type errors.
+
+```json
+"devDependencies": {
+    "typescript": "5.1.6"
+}
+```
+
+## Update `@types/node`
+
+Update `@types/node` to the `^20.3.1` version in `dependencies` in the `package.json` file.
+
+```json
+"dependencies": {
+    "@types/node": "^20.3.1"
+}
+```
+
+If the task does not use built-in Node.JS modules (such as `fs` or `path`) directly, remove `@types/node` from the task dependencies.
+
+## Update `task-lib` and `tool-lib`
+
+Update `azure-pipelines-task-lib` to `^4.13.0` and `azure-pipelines-tool-lib` to `^2.0.7` in `package.json` dependencies, if a task has these packages.
+
+`task-lib` package uses some shared (e.g. global object) resources to operate so it may cause unexpected errors in cases when more than one version of the package is installed for a task. This happens if `task-lib` in subdependencies of the task (e.g. in some common npm packages used by the task) has a different version than in dependencies of the task itself. Same for `tool-lib`.
+
+If the task uses `task-lib`, `tool-lib`, and some common npm packages that use `task-lib` and `tool-lib` as well, make sure `task-lib` and `tool-lib` have the same version in common npm packages as in the task itself.
+As a possible solution you also can remove these package versions via the `make.json` file, for example:
+
+```json
+{
+    "rm": [
+        {
+            "items": [
+                "node_modules/any-common-npm-package/node_modules/azure-pipelines-task-lib",
+                "node_modules/any-common-npm-package/node_modules/azure-pipelines-tool-lib"
+            ],
+            "options": "-Rf"
+        }
+    ]
+}
+```
+
+Here is [the repo with different common npm packages](https://github.com/microsoft/azure-pipelines-tasks-common-packages) that can be used in the task.
+
+## Add `Node20_1` handler
+
+Add a new `Node20_1` execution handler in the `task.json` file.
+
+<table>
+<tr>
+<th>From</th>
+<th>To</th>
+</tr>
+<tr>
+<td>
+
+```json
+"execution": {
+    "Node10": {
+        "target": "main.js",
+        "argumentFormat": ""
+    },
+    "Node16": {
+        "target": "main.js",
+        "argumentFormat": ""
+    }
+}
+```
+
+</td>
+<td>
+
+```json
+"execution": {
+    "Node10": {
+        "target": "main.js",
+        "argumentFormat": ""
+    },
+    "Node16": {
+        "target": "main.js",
+        "argumentFormat": ""
+    },
+    "Node20_1": {
+        "target": "main.js",
+        "argumentFormat": ""
+    }
+}
+```
+
+</td>
+</tr>
+</table>
+
+## Specify `minimumAgentVersion`
+
+If several handlers are specified in the `task.json` file, the highest one will be selected from handlers that are available on the certain agent. For example, if `Node10`, `Node16`, and `Node20_1` handlers are specified in the `task.json` file, and an old version of the agent (that is going to execute the task) has `Node` (version 6), `Node10`, and `Node16` handlers, then the `Node16` handler will be used. At the same time, the same agent will fail to execute the task if the `Node20_1` handler only is specified in the `task.json` file. Therefore you should specify `minimumAgentVersion`.
+
+`minimumAgentVersion` specified in the `task.json` file will trigger [an automatic upgrade](https://docs.microsoft.com/en-us/azure/devops/pipelines/agents/agents?view=azure-devops&tabs=browser#agent-version-and-upgrades) for agents less than the specified version.
+
+* [Agent version `2.144.0`](https://github.com/microsoft/azure-pipelines-agent/releases/tag/v2.144.0) is the first version that supports `Node10` handler. So set `minimumAgentVersion` at least to `2.144.0`.
+
+```json
+"minimumAgentVersion": "2.144.0"
+```
+
+* [Agent version `2.209.0`](https://github.com/microsoft/azure-pipelines-agent/releases/tag/v2.209.0) is the first version that supports `Node16` handler. If you want to run the task using at least `Node16` handler, set `minimumAgentVersion` to `2.209.0`.
+
+```json
+"minimumAgentVersion": "2.209.0"
+```
+
+* [Agent version `3.232.1`](https://github.com/microsoft/azure-pipelines-agent/releases/tag/v3.232.1) is the first version that supports `Node20_1` handler. If you want to run the task using `Node20_1` handler for sure, set `minimumAgentVersion` to `3.232.1`.
+
+```json
+"minimumAgentVersion": "3.232.1"
+```
+
+## Test the changes
+
+Test that the task works correctly on each execution handler specified in the `task.json` file.
+
+How to test the changes:
+* Run unit tests (they should pass on each handler specified in the `task.json` file).
+* Run pipeline with the task using `Node10` handler (if it is specified in the `task.json` file).
+* Run pipeline with the task using `Node16` handler (if it is specified in the `task.json` file).
+* Run pipeline with the task using `Node20_1` handler.
+
+To force the agent to use Node 10 handler for all Node-based tasks, set the pipeline variable / the agent environment variable `AGENT_USE_NODE10` to `true`.
+
+To force the agent to use Node 20 handler for all Node-based tasks, set the pipeline variable / the agent environment variable `AGENT_USE_NODE20_1` to `true`.
+
+## Feedback
+
+If you run into some issues while migrating to Node 20, please create a ticket with the label `node-migration: Node20`.