FEATURE: Update default branches during creation of new release branch

[ahaeslich]

As we don't use a master/main branch anymore the default branches should be switched during creation of the branches. The github api already supports this: https://docs.github.com/de/rest/repos/repos?apiVersion=2022-11-28#update-a-repository

Questions:

• Should this setting be editable to support the creation of new branches for e.g. a next major version which might not be the direct next release?
• Should we split this feature up into a separate script/job to enable it's usage to simply change the default_branch afterwards? The use case i'm thinking of is the Neos 9 release. We already have the branches in some repositories and it would be quite handy if we could switch multiple repositories at once at some point in the future.

This change might also be needed in neos/flow-development-distribution