Move release notes compiler to its own repository

[cortadocodes]

Summary

Move the release notes compiler to the new octue/generate-pull-request-description repo where it can be used as a GitHub action. It's also still available the old way, but support for this will be remove at some point.

Contents (#77)

Refactoring

• Move release notes compiler to https://github.com/octue/generate-pull-request-description

Fixes

• Fix installation of package in Dockerfile

Operations

• Avoid running python-ci workflow on main branch
• Ignore Codecov failure when releasing
• Fix context for check-semantic-version docker image builds
• Remove unnecessary setup-python steps in workflows
• Use new generate-release-notes GHA in update-pull-request workflow
• Use latest version of checkout GHA in workflows

[codecov-commenter]

Codecov Report

Merging #77 (ffcfda7) into main (df60f53) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #77   +/-   ##
=======================================
  Coverage   96.67%   96.67%           
=======================================
  Files           4        4           
  Lines         301      301           
=======================================
  Hits          291      291           
  Misses         10       10           

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