remove gradle

[dennisbader]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Fixes #1467, fixes #586, fixes #689

Summary

This is the last of a series of PRs to improve our CI/CD pipeline and remove gradle as a dependency.

• removes gradle dependency from darts

Related PRs: #2577, #2580, #2581, #2582, #2583

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.88%. Comparing base (ae04750) to head (769036f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2584      +/-   ##
==========================================
- Coverage   93.89%   93.88%   -0.02%     
==========================================
  Files         139      139              
  Lines       14888    14874      -14     
==========================================
- Hits        13979    13964      -15     
- Misses        909      910       +1     

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