feat: Add broken link checker

.github/ISSUE_TEMPLATE/broken-link-report.md

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+---
+name: Broken link report
+about: Automated issue template for reporting link checker fails
+title: Failing link check ({{ date | date('dddd, MMMM Do') }})
+labels: automated issue, bug, documentation, broken links
+---
+
+The broken link check failed. Check [the workflow logs](https://https://github.com/keptn-sandbox/new-keptn-docs-engine/actions/workflows/daily-link-checker.yaml) to identify the failing links.

.github/workflows/daily-link-checker.yaml

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+name: Check all markdown links daily
+
+on:
+  schedule:
+    - cron: '0 23 * * *'
+
+permissions:
+  contents: read
+  issues: write
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@master
+      - uses: gaurav-nelson/github-action-markdown-link-check@v1
+        # checks all markdown files from /docs including all subfolders
+        with:
+          use-quiet-mode: 'yes'
+          use-verbose-mode: 'yes'
+          config-file: '.github/workflows/markdown.links.config.json'
+          folder-path: 'docs/'
+      - uses: actions/checkout@master
+      - uses: gaurav-nelson/github-action-markdown-link-check@v1
+        # checks all markdown files from the root but ignores subfolders
+        with:
+          use-quiet-mode: 'yes'
+          use-verbose-mode: 'yes'
+          config-file: '.github/workflows/markdown.links.config.json'
+          max-depth: 0
+
+      # Automatically create an issue if there are broken links
+      - name: Create issue
+        if: ${{ failure() }}
+        uses: JasonEtco/create-an-issue@9e6213aec58987fa7d2f4deb8b256b99e63107a2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          filename: .github/ISSUE_TEMPLATE/broken-link-report.md

.github/workflows/markdown.links.config.json

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+{
+    "replacementPatterns": [
+      {
+        "pattern": "^/",
+        "replacement": "https://keptn-experimental-docs-site.netlify.app/"
+      }
+    ],
+    "ignorePatterns": [
+      {
+        "pattern": "^https?://localhost"
+      }
+    ]
+}