improved release instructions and workflow

[LucaMarconato]

The release process + keeping an up-to-date a changelog were too tedious, this is the new proposed approach, exemplified and explained in this video: https://www.loom.com/share/7097455bc0b9449fbe72d53fc778cbf9

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.79%. Comparing base (b285f5f) to head (c3c59ff).
Report is 53 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #817   +/-   ##
=======================================
  Coverage   91.79%   91.79%           
=======================================
  Files          45       45           
  Lines        7118     7118           
=======================================
  Hits         6534     6534           
  Misses        584      584           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[LucaMarconato]

PRs that are also to be merged to complete the transition across repos:

• improved release process spatialdata-io#254 (this I merged already because it's not removing the CHANGELOG.md, which is the biggest change)
• Improve release process documentation, part 2 spatialdata-io#255
• Improved the release process spatialdata-plot#400
• Improved release process and its documentation napari-spatialdata#338