Feat sharable testimonials endpoints

[abdullai-t]

Summary / Highlights

This PR contains:

• An endpoint for sharing testimonials with other communities
• An endpoint for listing testimonials from other communities
• Updated the testimonial creation and update endpoints to support the sharable testimonial feature
• Added new tests.

Details (Give details about what this PR accomplishes, include any screenshots etc)

Testing Steps (Provide details on how your changes can be tested)

run make test

Requirements (place an x in each [ ])

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've tested my changes manually.
• [ ] I've added unit tests to my PR.

Transparency (Project board)

• [x] I've given my PR a meaningful title.
• [x] I linked this PR to the relevant issue.
• [ ] I moved the linked issue from the "Sprint backlog" to "In progress" when I started this.
• [ ] I moved the linked issue to "QA Verification" now that it is ready to merge.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 74.09091% with 114 lines in your changes missing coverage. Please review.

Project coverage is 56.67%. Comparing base (78b333e) to head (11b1ed7). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/api/store/testimonial.py	64.88%	46 Missing :warning:
...rc/task_queue/nudges/testimonial_approval_nudge.py	27.77%	39 Missing :warning:
src/api/store/event.py	0.00%	12 Missing :warning:
src/task_queue/helpers.py	22.22%	7 Missing :warning:
src/database/models.py	78.26%	5 Missing :warning:
src/api/handlers/testimonial.py	91.17%	3 Missing :warning:
src/api/services/testimonial.py	81.81%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1162 +/- ## ========================================== + Coverage 56.45% 56.67% +0.22% ========================================== Files 470 473 +3 Lines 34433 34834 +401 ========================================== + Hits 19439 19743 +304 - Misses 14994 15091 +97 ```

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