Update E2E base image workflow to specify default value on input

Instead of defaulting the value when declaring the env var, do it
in the input. This means the value is displayed to the user before
they proceed and can be modified or overridden in the GitHub Actions
UI more easily if needed.

Author: AlanGreene

.github/workflows/e2e-base-image.yml

@@ -7,8 +7,10 @@ on:
   workflow_dispatch:
     inputs:
       tag:
-        description: 'Tag containing the Node.js and browser versions, e.g. node24.14.0-chrome140'
-        required: false
+        description: 'Image tag, typically containing the Node.js and browser versions'
+        required: true
+        default: 'node24.14.0-chrome147'
+        type: string
 
 concurrency:
   group: ${{ github.workflow }}
@@ -20,7 +22,7 @@ defaults:
 
 env:
   REGISTRY: ghcr.io
-  TAG: ${{ inputs.tag || 'node24.14.0-chrome147' }}
+  TAG: ${{ inputs.tag }}
 
 jobs:
   build:

packages/e2e/base-image/README.md

@@ -5,7 +5,7 @@
 To create a release:
 
 - verify the `CHROME_VERSION` and `NODE_VERSION` args in the [`Dockerfile`](./Dockerfile) on the main branch are correct
-- set a matching tag value in the `TAG` environment variable in the [workflow](../../../.github/workflows/e2e-base-image.yml), e.g. `node20.11.0-chrome121`
+- set a matching tag value for the `on.workflow_dispatch.inputs.tag.default` input in the [workflow](../../../.github/workflows/e2e-base-image.yml), e.g. `node20.11.0-chrome121`
 - manually trigger the [workflow](https://github.com/tektoncd/dashboard/actions/workflows/e2e-base-image.yml)
 - check the status of the resulting run
 - confirm the image was [released and properly tagged](https://github.com/tektoncd/dashboard/pkgs/container/dashboard%2Fdashboard-e2e-base)