feat: Argocd notification self service

[mayzhang2000]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.

[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (4875b02) 49.53% compared to head (4c910e6) 49.50%.
Report is 6 commits behind head on master.

Files	Patch %	Lines
util/notification/settings/settings.go	18.18%	17 Missing and 1 partial ⚠️
notification_controller/controller/controller.go	74.28%	8 Missing and 1 partial ⚠️
cmd/argocd/commands/admin/notifications.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #16488      +/-   ##
==========================================
- Coverage   49.53%   49.50%   -0.03%     
==========================================
  Files         269      269              
  Lines       47321    47430     +109     
==========================================
+ Hits        23441    23482      +41     
- Misses      21576    21643      +67     
- Partials     2304     2305       +1     

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