feat(github): add workflow_dispatch to the GitHub notification service

[yugstar]

Closes #442

What

Adds a workflowDispatch option to the GitHub notification service so a notification can trigger a GitHub Actions workflow dispatch event.

The service already supported repository_dispatch (#393); workflow_dispatch was the remaining half of #442.

Usage

template.app-deployed: |
  github:
    workflowDispatch:
      workflow: deploy.yml
      ref: "{{.app.spec.source.targetRevision}}"
      inputs: |
        {
          "application": "{{.app.metadata.name}}",
          "revision": "{{.app.status.operationState.syncResult.revision}}"
        }

• workflow — the workflow file name (e.g. deploy.yml) or its ID.
• ref — the branch or tag the workflow runs from.
• inputs — optional JSON object of workflow inputs (templated, then decoded into the inputs map).

The GitHub App / token needs the actions: write permission.

Implementation

Mirrors the existing repositoryDispatch design end to end:

• New GitHubWorkflowDispatch struct + workflowDispatch field on GitHubNotification.
• Templater parses/executes workflow, ref, and inputs (the inputs JSON string is templated then json.Unmarshal-ed into the inputs map, just like repositoryDispatch.clientPayload).
• New actionsService interface + GetActions() on the githubClient interface and adapter, calling Actions.CreateWorkflowDispatchEventByFileName (go-github v69).
• Docs section + example.

Tests

• TestGetTemplater_Github_WorkflowDispatch — verifies workflow, ref, and inputs template correctly.
• TestGitHubService_Send_WorkflowDispatch — verifies the dispatch is sent with the right workflow file, ref, and decoded inputs map.

go build, go vet, gofmt, and the full pkg/services test suite pass.

[codecov]

Codecov Report

❌ Patch coverage is 57.14286% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.13%. Comparing base (da04400) to head (f4bf039).
⚠️ Report is 37 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/services/github.go	57.14%	10 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #459      +/-   ##
==========================================
+ Coverage   55.41%   57.13%   +1.72%     
==========================================
  Files          46       49       +3     
  Lines        4125     3824     -301     
==========================================
- Hits         2286     2185     -101     
+ Misses       1511     1273     -238     
- Partials      328      366      +38     

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[yugstar]

For context on why this is worth having alongside the existing repository_dispatch support (#393): the two cover different needs.

• repository_dispatch sends a custom event type + payload that a workflow must subscribe to via on: repository_dispatch and then parse.
• workflow_dispatch runs a specific workflow file directly on a chosen ref, with typed inputs — the same as the "Run workflow" button in the UI. No custom event wiring needed.

The original issue (#442) asked for both, and this completes the second half. The implementation mirrors repository_dispatch exactly (struct + templater + a new actionsService on the client interface + Send), with tests and docs.