Prepare for 6.1

[mauritsvanrees]

I want to release the first alpha of Plone 6.1 this week:
plone/Products.CMFPlone#3894

Is there anything that needs to be prepared for the Docker images?
I guess for starters a 6.1.x branch would be needed in this repo.

Note that https://dist.plone.org/release/6.1-dev/ exists since October (no changes since then as far as I remember), so some experiments are already possible.

[jensens]

I think we can close this?

[jensens]

oh, no, ther is no 6.1.0 branch yet, sorry

[jensens]

btw, where is the 6.1 image stuff? I can not find anything in here? cc @ericof