Test the rolling update support for BC changes

[phavekes]

This issue is imported from pivotal - Originaly created at Nov 26, 2019 by bstrooband

I think we should test the rolling update support (BC schema changes) in order to prevent a lot of overhead to fix a broken release.

I think it would be very valuable to test the rolling updates because a lot of effort is undertaken when implementing a feature with rolling update support. In practice we see that a lot of knowledge is lost over time when the actual cleanup is released often months after the actual work was done.

Because this type of release strategy could break releases before the actual release and it proves very time consuming to manually test this it would be very valuable to have this kind of test.

Maybe we could use actions for this to test and directly build a release when a tag is set.
https://github.com/OpenConext/OpenConext-engineblock/actions

But then we probably need to discuss the pros and cons of the various release strategies:

• locally on a development VM
• on a Github shared runner
• on a private self hosted runner
  etc. etc.

We need to be aware that for the removal of a column we need three releases because annotations are used in Doctrine.

• remove column, while supporting old and new situation in code
• remove column, remove old code, but keep annotations to support query building in old releases.
• remove annotations