Update/improve guidance re. releases

[mary-cleaton]

The Tag new releases section in the version control section represents an old way of doing releases. E.g. doing releases via tags was superseded in GitLab in version 11.9 (Jan 2019).

I'd like:

1. Automated releases to be the default Duck book way of doing releases, rather than tags.
2. Discussion of related CI/CD processes, e.g. maintaining a change log, added to this section.
3. Automated releases to be required by the Duck book for all pipelines (in addition to having releases of the data output of the product). The code release number should be cited in the product release notes.

I think points 1 and 2 will bring us up to current practice with doing releases and point 3 will allow better cross-referencing and citing of current and historic pipeline code with pipeline outputs, particularly as they mature into production.

I think releases via tags / other manual methods can still be mentioned in the Duck book, but I don't think they should be the sole recommended way of doing releases. I also think it should be noted that they are an outdated way of doing releases.

If possible, I think Duck book updaters should also collaborate with DAPCATS to ensure that there is, at minimum, a tutorial for ONS staff on how to do automated and manual releases via the currently recommended systems for both GitLab and GitHub. This should also probably be accompanied by training about Git branching strategies, as releases work best when you are using a more complex Git strategy such as GitFlow that has both a main and development branch in addition to feature branches.

In relation to this issue, the following may be helpful:

• GitLab documentation: Releases
• StackOverflow Question "How to create releases in GitLab?"
• GitHub documentation: Managing releases in a repository
• talk to RDSA team, who have automated releases set up in their GitHub repository.