Update release schedule

[zklaus]

This updates the release schedule with past releases, thus highlighting the next upcoming release.

Closes #1947

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Checklist for technical review

• Create an issue to discuss what you are going to do, if you haven't done so already (and add the link at the bottom)
• The pull request has a descriptive title that can be used as a one line summary in the changelog
• Documentation is available
• Circle/CI tests pass. If the tests are failing, click the Details link to find out why.
• Preferably Codacy code quality checks pass, however a few remaining hard to solve Codacy issues are still acceptable. If there is an error, click the link to find out why. If you suspect Codacy may be wrong, please ask by commenting.
• The documentation is building successfully on readthedocs and looks well formatted, click the Details link to see it.

[zklaus]

This depends on ESMValGroup/ESMValCore#899 to provide labels for the links to the core changelog. When that is merged, we can fix the circleci complaints about the missing link target.

[zklaus]

Hmm. The links to the core changelog don't appear quite right, though the build error is gone. Not sure what's going on. One of you sphinx gurus have an opinion or advice?

[zklaus]

@nielsdrost could you update the illustration? If it's easy to do. Otherwise, we'll keep it as an example and perhaps update it later.

[valeriupredoi]

@nielsdrost could you update the illustration? If it's easy to do. Otherwise, we'll keep it as an example and perhaps update it later.

I suggested in the issue to have the code that plots that plot with release goal posts be included in the utils or something; if not I might write a code that plots those, but you may regret that since the moving targets for the next releases may be tanks 😀

[valeriupredoi]

cheers @zklaus - I'll have a looksee myself tomorrow 👍

[bouweandela]

Hmm. The links to the core changelog don't appear quite right, though the build error is gone. Not sure what's going on. One of you sphinx gurus have an opinion or advice?

You're the sphinx guru here @zklaus, I didn't know you could make the links like that! It looks great to me, maybe it just looks wrong because of some caching? sometimes it helps if you add a ? followed by some random characters to the URL to trick the page into reloading.

[zklaus]

You are right, now it looks ok also for me; probably some caching issue. Last thing is then @nielsdrost's graphic, otherwise, I am happy with this PR.

[valeriupredoi]

finally got around to generate the dox and have a look - very nice! Lots of useful info 👍 🍺

[zklaus]

Seems Niels is busy or on Christmas break already. Since the figure is clearly labeled as an example, I suggest merging this PR as-is and setting up a workflow for updating the graphic for every future release separately.

[valeriupredoi]

@bouweandela is on hols too and I will be gonzo from tomorrow myself, so my last PR approval of the year 🎅