[MNT] changelog generator script and release workflow improvement

[fkiraly]

• add changelog generator script as used in sktime
• straighten out the release workflow so wheels build is required for test phase
• changes release to be API token based

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.14%. Comparing base (edc8329) to head (fe4e94d).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1659   +/-   ##
=======================================
  Coverage   90.14%   90.14%           
=======================================
  Files          32       32           
  Lines        4780     4780           
=======================================
  Hits         4309     4309           
  Misses        471      471           

Flag	Coverage Δ
cpu	90.14% <ø> (ø)
pytest	90.14% <ø> (ø)

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