Fix broken integration API update for various fields

What does this MR do and why?

This MR has been split from !122943 (closed).

This MR fixes various bugs in the project integration API:

• Fix broken update for confidential_note_channel (#23479, #28903 (comment 272724550))
• Fix broken update for job_events and commit_events (#196573)

Fixes #23479 and #196573

How to set up and validate locally

1. Enable slack integration on a project (can be done via the web UI).
2. Try changing the any previously mentioned field on the /api/v4/projects/$PROJECT_ID/integrations/slack endpoint.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.