V2 support branch

[muhlemmer]

We have recently released V3 on main, which brings some breaking changes. There will be a period where V2 will be supported.

• 2.11.x is branched from the last commit bb115d8 before V3.
• It will receive security and (simple) bug fixes.
• Community should lead contributions to the V2 branch. Zitadel members will do the reviews as usual.
• There is no specific timeline (yet) but as long as people will send fixes, we don't mind merging them.
• No new features, those should target main.
• Breaking changes should target next.

The above should off course be integrated in the contribution guidelines, which we will do in due time.

I will create the branch today and will take care of some first chores:

• auto releases
• branch protection

From there on, it should become a community effort.