feat(gl-set-slack): configure the GitLab for Slack app (per-event channels)

otica-resolverrequested to merge
agent/issue-7 into main

Closes #7 (closed) (follow-up to #6 (closed)).

What

Adds a GitLab for Slack app mode to gl-set-slack, alongside the existing legacy webhook service.

  • New target gl-set-slack-app (no vault-login prereq — the app needs no webhook/Vault) → PUT projects/:id/integrations/gitlab-slack-application.
  • New slack_app_json() payload: per-event channels (issue_channel, note_channel, merge_request_channel, push_channel, tag_push_channel, pipeline_channel, deployment_channel, job_channel, wiki_page_channel, confidential variants), each defaulting to SLACK_GITLAB_CHANNEL and CI/CD events (pipeline/job) to SLACK_CICD_CHANNEL. Channel vars are bare names; the script adds the # (matching SLACK_GITLAB_CHANNEL).
  • Omits work_item_channel (silently ignored by the current GitLab — per the issue caveat).
  • Reports which integration was modified; errors out (exit 1) with the API message on failure.
  • The script still honors SLACK_APP=true when invoked directly; gl-set-slack (legacy) is unchanged and its #6 (closed) warning now points at gl-set-slack-app.

Why

#6 (closed) only added a warning for Slack-app repos; #7 (closed) makes the app actually configurable from OTICA.

Testing

  • bash -n + make validate pass.
  • App JSON renders as valid JSON with #-prefixed per-event channels, no webhook, no work_item_channel; pipeline/job route to the CI/CD channel.
  • End-to-end against a live Slack-app repo not exercised (no such repo available — noted in the issue); the API path/fields follow the documented gitlab-slack-application integration.

Self-reviewed (3 rounds): channel #-convention documented, vault-free target added so app mode needs no Vault.

Closes #7 (closed)

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