docs: test broken links in website (#1912)

The action triggers manually as a first step to test this functionality. In the near future, we might schedule it

.github/workflows/build_doc_prs.yaml

@@ -7,7 +7,6 @@ on:
 
 jobs:
   validate:
-
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3

.github/workflows/check_links.yaml

@@ -0,0 +1,55 @@
+name: Check links
+
+on:
+  workflow_dispatch:
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      issues: write
+    env:
+      issue-lookup-label: automated-link-issue
+      issue-content: ./lychee-out.md
+    steps:
+      - uses: actions/checkout@v3
+      - name: Restore lychee cache
+        uses: actions/cache@v3
+        with:
+          path: .lycheecache
+          key: cache-lychee-${{ github.sha }}
+          restore-keys: cache-lychee-
+      - name: Link Checker
+        id: lychee
+        uses: lycheeverse/lychee-action@v1.5.0
+        with:
+          fail: true
+          args: '"./website/docs/**/*.md" "./website/docs/**/*.mdx" "./src/mailtemplates/*.mustache" --scheme http --scheme https --cache --max-cache-age 7d --exclude-mail --verbose' # other excludes are in .lycheeignore
+          output: ${{ env.issue-content }}
+
+      # Permissions (issues: read)
+      - name: 'Look for an existing issue'
+        if: ${{ failure() }}
+        id: last-issue
+        uses: micalevisk/last-issue-action@v2
+        # Find the last updated open issue with a `automated-issue` label:
+        with:
+          state: open
+          labels: ${{ env.issue-lookup-label }}
+
+      # Permissions (issues: write)
+      - name: 'Create a new issue, or update an existing one'
+        if: ${{ failure() }}
+        uses: peter-evans/create-issue-from-file@v4
+        with:
+          title: 'docs: Broken links found'
+          content-filepath: ${{ env.issue-content }}
+          # Update an existing issue if one was found (issue_number),
+          # otherwise an empty value creates a new issue:
+          issue-number: ${{ steps['last-issue']['outputs']['issue-number'] }}
+          # Add a label(s) that `last-issue` can use to find this issue,
+          # and any other relevant labels for the issue itself:
+          labels: |
+            ${{ env.issue-lookup-label }}
+            docs

.lycheeignore

@@ -0,0 +1,20 @@
+dev-example-okta.com
+.*-dsn.algolia.net
+www.linkedin.com/company/getunleash
+
+.*.unleash.host.*.com.*
+unleash.*.com/api/
+secure-unleash.herokuapp.com
+
+localhost
+changeme
+hostname
+unleash:4242
+user:password@url
+your.heroku.instance.com
+your-api-url
+version.unleash.run
+
+datadog.*/api/v1/events
+ddog.*/api/v1/events
+api.datadoghq.com