Clear release notes and migration script (#591)

Author: llucax

RELEASE_NOTES.md

@@ -2,10 +2,12 @@
 
 ## Summary
 
-This release focuses on finishing the automation of dependabot updates, adding more automated upgrade workflows and fixing some problems with the previous release.
+<!-- Here goes a general summary of what this release is about -->
 
 ## Upgrading
 
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+
 ### Cookiecutter template
 
 All upgrading should be done via the migration script or regenerating the templates.
@@ -14,28 +16,22 @@ All upgrading should be done via the migration script or regenerating the templa
 curl -sSLf https://raw.githubusercontent.com/frequenz-floss/frequenz-repo-config-python/<tag>/cookiecutter/migrate.py | python3 -I
 ```
 
+But you might still need to adapt your code:
+
+<!-- Here upgrade steps for cookiecutter specifically -->
+
 ## New Features
 
+<!-- Here goes the main new features and examples or instructions on how to use them -->
+
 ### Cookiecutter template
 
-- The cookiecutter now asks whether a repository is private, defaults that answer from the selected license, and uses it to toggle private-repository workflow behavior, public publishing jobs, and the link to GitHub Discussions in the issue template chooser.
-- All dependencies have been updated in the templates.
-- API projects now ship a dedicated `grpc-migration.yaml` workflow that runs after Dependabot bumps `grpcio`/`grpcio-tools`/`protobuf` and rewrites the matching runtime `>=` floors in `pyproject.toml`.
-- API projects now have a better grpcio/protobuf updates grouping in Dependabot, which should make upgrading easier, and plays nicer with the new `grpc-migration.yaml` workflow.
-- API projects should now use the new API-specific *Protect version branches* ruleset variant, which includes the required `Fix gRPC/protobuf runtime floors` check without affecting non-API Python projects.
-- Workflows using the `gh-action-dependabot-migrate` are upgraded to the latest version, which avoids unnecessary version iterations.
-- Add an `isort-migration.yaml` workflow that automatically reorders imports when Dependabot upgrades `isort`.
+<!-- Here new features for cookiecutter specifically -->
 
 ## Bug Fixes
 
+<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+
 ### Cookiecutter template
 
-- The unused cross-arch QEMU-based testing infrastructure has been removed. The `.github/containers/nox-cross-arch/` and `.github/containers/test-installation/` directories, as well as the "Cross-Arch Testing" section in `CONTRIBUTING.md`.
-- Private repositories now are generated with credentials uncommented and the publishing workflows disabled.
-- The issue template chooser (`config.yml`) no longer includes the `contact_links` section for private repositories, since GitHub Discussions are typically disabled for them.
-- Normalized the GitHub Action hashes for `gh-action-setup-git` and `gh-action-setup-python-with-deps` to point to the actual commit object, which is what Dependabot expects.
-- API projects now configure black with `extend-exclude = '^/submodules/'` so the formatting check doesn't descend into external git submodules that don't follow our formatting rules.
-- API projects now configure isort with `skip_glob = ["submodules/*"]` so the import-sorting check doesn't descend into external git submodules that don't follow our rules.
-- `CONTRIBUTING.md`
-  * Fixed the nox example commands in  to use the correct `tests/` directory instead of the non-existent `test/` directory.
-  * Fixed the wrong mention to PyPI publishing when releasing for private repositories.
+<!-- Here bug fixes for cookiecutter specifically -->