Fix: [Actions] changelog assumed major.minor.patch versioning (#9482)

We now use major.minor versioning, so it failed to pick up the
correct information.

Add: [Actions] release workflow for both releases and nightlies

This has several ways of being triggered:
- When creating a new release via the GitHub interface. Fully
automated that will produce new binaries, upload them, and it
will even update the website to tell about the new version.
- When triggered in an automated way from OpenTTD/workflows to
start a nightly.
- Manually via the Release workflow, which accepts branches,
Pull Requests and tags to build.

Rerunning a job is safe and should be without issues. Everything
retriggers and updates what-ever might have been broken. In fact,
except for dates, it should produce identical results.

Co-authored-by: Charles Pigott <charlespigott@googlemail.com>