Improve the ESMValCore release documentation

[ehogan]

Is your feature request related to a problem? Please describe.

@chrisbillowsMO and I are currently working on the ESMValCore release, see #2389. There are a few items not detailed in the ESMValCore documentation: Making a release instuctions that might be worth adding:

We recognise that a lot of this information already exists but we did struggle to understand the process in places. The order confused as at times and some of the specific we found out from conversation would have helped us a lot if they were included in the documentation.

We'd have found it easier to follow overall if there were perhaps more short, individual pages each focused on a clearly delineated individual step.

Also, it would've been useful if there was a concise outline very early in the instructions that outlined every time sensitive step.

As specific suggestions, we'd first propose it might be helpful if this page offers the release a brief, high level overview of the entire process, including:

• Introduction/overview of ESMValTool approach to releases (which is currently on this [page] (https://docs.esmvaltool.org/en/latest/community/release_strategy/release_strategy.html).
• Overview of the release process (e.g. diagram, similar to detailed timeline steps)
• Pre-requisites
• Community Interactions
• Create ESMValCore rc1
• ESMValCore Testing
• Appendix 1: Calendar (previous releases)

When the "feature freeze" date has been determined:

• [ ] Add the due date to the milestone for ESMValCore.
• [ ] Update the release schedule, see e.g. https://github.com/ESMValGroup/ESMValTool/issues/3572 / https://github.com/ESMValGroup/ESMValTool/pull/3573.
• [ ] Create and pin an ESMValCore discussion, see e.g. #2389.

At least two weeks before the proposed "feature freeze" date:

• [ ] Comment on any issues and PRs in the milestone to inform the assignees of the "feature freeze" date.

Would you be able to help out?

Yes 😊