feat: add user-defined context to notifications

[daftping]

Fixes #2595
Aligns with Argo CD supported notification configurations https://argo-cd.readthedocs.io/en/stable/operator-manual/notifications/templates/#defining-user-defined-context

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional with a list of types and scopes found here, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I've signed my commits with DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 78.20%. Comparing base (8405f2e) to head (dca652b).
Report is 102 commits behind head on master.

Files	Patch %	Lines
utils/record/record.go	70.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3553      +/-   ##
==========================================
- Coverage   81.83%   78.20%   -3.64%     
==========================================
  Files         135      158      +23     
  Lines       20688    18402    -2286     
==========================================
- Hits        16931    14391    -2540     
- Misses       2883     3102     +219     
- Partials      874      909      +35     

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[github-actions]

Go Published Test Results

2 161 tests   2 161 ✅  2m 53s ⏱️
  119 suites      0 💤
    1 files        0 ❌

Results for commit dca652b.

[github-actions]

E2E Tests Published Test Results

  4 files    4 suites   3h 27m 5s ⏱️
110 tests  97 ✅  6 💤  7 ❌
460 runs  416 ✅ 24 💤 20 ❌

For more details on these failures, see this check.

Results for commit dca652b.