chore: Bump Kotlin to 2.1.0

[thomaspoignant]

Description

Bump Kotlin to 2.1.0.
Since I am not sure if we should bump now I will keep the PR open for a while.

Checklist

• I have tested this code
• I have followed the contributing guide

[netlify]

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[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

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[sonarqubecloud]

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 SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.72%. Comparing base (c815c48) to head (732f199).
⚠️ Report is 724 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2892   +/-   ##
=======================================
  Coverage   84.72%   84.72%           
=======================================
  Files         113      113           
  Lines        5237     5237           
=======================================
  Hits         4437     4437           
  Misses        634      634           
  Partials      166      166           

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[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.