Add Congo holidays

[PPsyrius]

Proposed change

Add Congo holidays with en_US, fr localization.

Resolves #1165 .

Type of change

• [x] New country/market holidays support (thank you!)
• [ ] Supported country/market holidays update (calendar discrepancy fix, localization)
• [ ] Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• [ ] Dependency update (version deprecation/pin/upgrade)
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] Breaking change (a code change causing existing functionality to break)
• [ ] New feature (new python-holidays functionality in general)

Checklist

• [x] I've followed the contributing guidelines
• [x] I've run make pre-commit, it didn't generate any changes
• [x] I've run make test, all tests passed locally

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (7c69ef0) to head (2b19e14). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #2037 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 189 190 +1 Lines 11486 11516 +30 Branches 1795 1797 +2 ========================================= + Hits 11486 11516 +30 ```

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