feat!: convert reusable workflows to composite actions

[vaind]

Summary

Convert the updater and danger reusable workflows to composite actions to address script download reliability issues and simplify usage.

Key Changes

• 🔄 Convert workflows to actions: Replace .github/workflows/updater.yml and .github/workflows/danger.yml with updater/action.yml and danger/action.yml composite actions
• 📦 Bundle scripts locally: All PowerShell and JavaScript files are now bundled with the actions instead of downloaded at runtime
• 🧪 Update integration tests: Test workflows now use local actions (./updater, ./danger)
• 🔐 Input conversion: Convert secrets.api-token to inputs.api-token for the updater action
• 🗑️ Remove internal parameter: _workflow_version parameter no longer needed

Breaking Changes

Before (reusable workflow):

jobs:
  update-deps:
    uses: getsentry/github-workflows/.github/workflows/updater.yml@main
    with:
      path: my-dependency
      name: My Dependency
    secrets:
      api-token: ${{ secrets.GITHUB_TOKEN }}

After (composite action):

jobs:
  update-deps:
    runs-on: ubuntu-latest
    steps:
      - uses: getsentry/github-workflows/updater@main
        with:
          path: my-dependency
          name: My Dependency
          api-token: ${{ secrets.GITHUB_TOKEN }}

Benefits

• ✅ Faster execution: No script downloading during runtime
• ✅ Better reliability: Scripts bundled with action version
• ✅ Simpler usage: Direct action reference vs workflow path
• ✅ Version coupling: Action version matches script version

Test Plan

• Create composite action metadata files
• Bundle all required scripts locally
• Update integration test workflows
• Verify all inputs/outputs are preserved
• Remove old reusable workflows

Closes #113

🤖 Generated with Claude Code

[vaind]

@sentry review