prepare release

[janfb]

• add release template.
• add changelog etc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.41%. Comparing base (d3f22b5) to head (7bcc9c4).
Report is 6 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1337       +/-   ##
===========================================
- Coverage   89.40%   78.41%   -11.00%     
===========================================
  Files         118      118               
  Lines        8715     8748       +33     
===========================================
- Hits         7792     6860      -932     
- Misses        923     1888      +965     

Flag	Coverage Δ
unittests	78.41% <100.00%> (-11.00%)	⬇️

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Files with missing lines	Coverage Δ
sbi/__version__.py	100.00% <100.00%> (ø)

... and 34 files with indirect coverage changes

[janfb]

GPU tests are passing locally ✅