ci: add require multiple reviewers action (#204)

Requires a specified number of reviewers for certain important files,
the files are to be provided as an `important-files-path` var.

See `README.md` for more details
https://github.com/dequelabs/axe-api-team-public/pull/204/files#diff-db32ad4c1ae8b5f09def402ee7d7876046a269ae8c7b5bfb42567d703807902b

**NOTE:** this version doesn't account for edge cases like accounting
for approvals from people who requested changes, e.g. if a PR requires 2
reviewers, 1 reviewer requested changes but other 2 reviewers approved
the PR, the action will pass.

1. This would show a `Tests / require-multiple-reviewers` check that
would fail until a required number of reviewers approves a PR that uses
the action.
2. Also shows annotations on the files that are important. Annotations
remain on the files for information purposes and are not removed.

**Changes requested:**
<img width="842" alt="Tests / require-multiple-reviewers` fails since
the PR requires 1 reviewer and changes are requested"
src="https://github.com/user-attachments/assets/f9f49afa-6a23-4839-a374-f92eb9d387de"
/>

**Changes approved:**
<img width="842" alt="Tests / require-multiple-reviewers` passes since
the PR requires 1 reviewer and it's approved by 1 reviewer"
src="https://github.com/user-attachments/assets/ee1bfdd5-9f9d-405c-9f42-89409c7ecd41"
/>

**Annotations:**
<img width="1354" alt="`Annotation on an important file 'The file
important.txt is important and requires at least 1 reviewers.'"
src="https://github.com/user-attachments/assets/9f9a273a-8830-4ae1-9c3c-1625f7c2d542"
/>

Ref: dequelabs/axe-linter#1632

.gitattributes

@@ -0,0 +1,3 @@
+* text=auto eol=lf
+
+**/dist/** -diff linguist-generated=true

.github/actions/require-multiple-reviewers-v1/README.md

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+# require-multiple-reviewers-v1
+
+A GitHub Action that requires multiple reviewers for important files
+
+## Inputs
+
+| Name                   | Required | Description                                                                                                                              | Default |
+| ---------------------- | -------- | ---------------------------------------------------------------------------------------------------------------------------------------- | ------- |
+| `token`                | Yes      | A GitHub token with the [required permissions](#permissions)                                                                             | NA      |
+| `number-of-reviewers`  | Yes      | The number of reviewers required.                                                                                                        | 2       |
+| `important-files-path` | Yes      | The path to the file containing a list of important files. It should comply with [gitignore syntax](https://git-scm.com/docs/gitignore). | NA      |
+
+## Example usage
+
+```yaml
+name: Require multiple reviewers
+
+# This must be both pull_request and pull_request_review.
+# pull_request - for when the PR is initially created (or files are changed)
+# pull_request_review - for when the count of reviews on a PR changes
+on:
+  pull_request:
+  pull_request_review:
+
+jobs:
+  require-multiple-reviewers:
+    runs-on: ubuntu-latest
+    timeout-minutes: 2
+    permissions:
+      pull-requests: read
+      contents: read
+      checks: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Require two reviewers for important files
+        uses: dequelabs/axe-api-team-public/.github/actions/require-multiple-reviewers-v1@main
+        with:
+          token: ${{ github.token }}
+          number-of-reviewers: 2
+          important-files-path: .github/important-files.txt
+```
+
+## Permissions
+
+This action requires the following permission scopes:
+
+- `pull-requests: read` - To get pull request reviews.
+- `contents: read` - To read the contents of the repository, including the changed and important files.
+- `checks: write` - To create and update check runs with the results of the action.

.github/actions/require-multiple-reviewers-v1/action.yml

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+name: Require multiple reviewers
+description: Require multiple reviewers for important files
+
+# Define your inputs here.
+inputs:
+  token:
+    description: 'A GitHub token with the required permissions'
+    required: true
+  number-of-reviewers:
+    description: 'The number of reviewers required.'
+    required: true
+    default: '2'
+  important-files-path:
+    description: 'The path to the file containing a list of important files (gitignore syntax supported).'
+    required: true
+
+runs:
+  using: node20
+  main: dist/index.js