feat: add getMetadataValues for projects

[AmanuelAaron]

Ticket

ET-226

Description

Add getMetadataValues endpoints which fetches all unique metadata values for a given key in a given project. This only applies to metadata values that are string typed.

Test Plan

Checklist

• Changes have been manually QA'd
• New features have been approved by the corresponding PM
• User-facing API changes have the "User-facing API Change" label
• Release notes have been added as a separate file under docs/release-notes/
  See Release Note for details.
• Licenses have been included for new code which was copied and/or modified from any external code

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[codecov]

Codecov Report

Attention: Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.

Project coverage is 52.89%. Comparing base (0a57cde) to head (5e6cdbc).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9618      +/-   ##
==========================================
- Coverage   52.91%   52.89%   -0.03%     
==========================================
  Files        1255     1255              
  Lines      153086   153105      +19     
  Branches     3230     3229       -1     
==========================================
- Hits        81004    80978      -26     
- Misses      71931    71976      +45     
  Partials      151      151              

Flag	Coverage Δ
backend	44.01% <84.21%> (-0.07%)	⬇️
harness	72.76% <ø> (ø)
web	51.30% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
master/internal/api_project.go	36.83% <84.21%> (+1.45%)	⬆️

... and 8 files with indirect coverage changes

[corban-beaird]

Looks good! One last small nit, but it's non-blocking

[ashtonG]

web changes ok!