feat: Adding flag hashes in /v1/flag/change API

[thomaspoignant]

Description

In this PR we start returning an array of hashes (as uint32) for each flag.
It will allow server providers to store those hashes and compare them when a change is detected to be able to emit a flag change event with the information of which flag has changed.

See #2404 for more details.

Closes issue(s)

Resolve #2404

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.20%. Comparing base (fde9fff) to head (fb8f94a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2492      +/-   ##
==========================================
+ Coverage   86.18%   86.20%   +0.01%     
==========================================
  Files         100      100              
  Lines        3526     3530       +4     
==========================================
+ Hits         3039     3043       +4     
  Misses        360      360              
  Partials      127      127              

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[sonarcloud]

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