Add Samoa holidays

[kasya]

Proposed change

Add Samoa holidays

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

[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (96823e8) to head (f41e6d8). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #1914 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 185 186 +1 Lines 11263 11289 +26 Branches 1785 1785 ========================================= + Hits 11263 11289 +26 ```

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[kasya]

@kasya , it's great: 150 countries, a significant number! 👍 Please take a look at a few suggestions. :)

@KJhellico Thanks for the review! 👍🏼

[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