Add update-link-index action (#207)

## Changes

Add a new custom action named `update-link-index`.

## Related issues:

- depends on #164
- closes #163

---------

Co-authored-by: Martijn Laarman <[email protected]>

Author: reakaleek

actions/update-link-index/README.md

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+<!-- 
+    this documentation was generated by https://github.com/reakaleek/gh-action-readme 
+    with the command `VERSION=main gh action-readme update`    
+-->
+
+# <!--name-->Update Link Index<!--/name-->
+
+<!--description-->
+This action updates the link index for the given link reference file.
+<!--/description-->
+
+## Inputs
+
+<!--inputs-->
+| Name                  | Description                                                    | Required | Default                           |
+|-----------------------|----------------------------------------------------------------|----------|-----------------------------------|
+| `link_reference_file` | The path to the link reference file                            | `false`  | `.artifacts/docs/html/links.json` |
+| `aws_account_id`      | The AWS account ID to generate the role ARN for                | `false`  | `197730964718`                    |
+| `aws_region`          | The AWS region to use                                          | `false`  | `us-east-1`                       |
+| `aws_s3_bucket_name`  | The name of the S3 bucket to upload the link reference file to | `false`  | `elastic-docs-link-index`         |
+<!--/inputs-->
+
+## Outputs
+<!--outputs-->
+| Name | Description |
+|------|-------------|
+<!--/outputs-->
+
+## Usage
+
+<!--usage action="elastic/docs-builder/actions/update-link-index" version="env:VERSION"-->
+```yaml
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - "*.*.*"
+
+permissions:
+  contents: read
+  packages: write
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    permissions:
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{steps.deployment.outputs.page_url}}
+    steps:
+      - name: Publish Github
+        uses: elastic/docs-builder/actions/publish@main
+        id: deployment 
+
+      - name: Update Link Index
+        uses: elastic/docs-builder/actions/update-link-index@main
+```
+<!--/usage-->

actions/update-link-index/action.yml

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+name: Update Link Index
+
+description: |
+  This action updates the link index for the given link reference file.
+
+inputs:
+  link_reference_file:
+    description: 'The path to the link reference file'
+    required: false
+    default: '.artifacts/docs/html/links.json'
+  aws_account_id:
+    description: 'The AWS account ID to generate the role ARN for'
+    required: false
+    default: '197730964718' # elastic-web
+  aws_region:
+    description: 'The AWS region to use'
+    required: false
+    default: 'us-east-1'
+  aws_s3_bucket_name:
+    description: 'The name of the S3 bucket to upload the link reference file to'
+    required: false
+    default: 'elastic-docs-link-index'
+
+runs:
+  using: composite
+  steps:
+    - name: Update Link Index
+      run: |
+        echo "Updating link index"
+    - name: Generate AWS Role ARN
+      id: role_arn
+      shell: python
+      env:
+        AWS_ACCOUNT_ID: ${{ inputs.aws_account_id }}
+      run: |
+          import hashlib
+          import os
+
+          prefix = "elastic-docs-link-index-uploader-"
+          aws_account_id = os.environ["AWS_ACCOUNT_ID"]
+
+          m = hashlib.sha256()
+          m.update(os.environ["GITHUB_REPOSITORY"].encode('utf-8'))
+          hash = m.hexdigest()[:64-len(prefix)]
+          with open(os.environ["GITHUB_OUTPUT"], "a") as f:
+            f.write(f"result=arn:aws:iam::{aws_account_id}:role/{prefix}{hash}")
+    - name: Configure AWS Credentials
+      uses: aws-actions/configure-aws-credentials@e3dd6a429d7300a6a4c196c26e071d42e0343502 # v4.0.2
+      with:
+        role-to-assume: ${{ steps.role_arn.outputs.result }}
+        aws-region: us-east-1
+    - name: Upload Link Reference File to S3
+      bash: shell
+      run: |
+        repository_name=$(basename "${GITHUB_REPOSITORY}")
+        aws s3 cp ${{ inputs.link_reference_file }} "s3://${{ inputs.aws_s3_bucket_name }}/${repository_name}.json"