V1 support branch

[muhlemmer]

We have recently release V2 on main, which brings many breaking changes. There are requests to maintain a V1 branch for the time being. At Zitadel we have nothing against it, however there is a "policy" we would like to share:

• V1 will be branched from the latest tag.
• It will receive security and (simple) bug fixes.
• Community should lead contributions to the V1 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 fork today and will take care of some first (urgent) chores:

• drop Go support <1.18 : x/text updates don't build against older releases.
• update all modules. Due to the above, some dependabot PRs couldn't be merged into V1 / old main.
• auto releases
• branch protection

From there on, it should become a community effort.

[muhlemmer]

With the release of v3 we've created a v2 support branch. V1 has received one last update of the go.mod deps and this is released under v1.13.5 this morning. This is the last v1 release and users should definitely upgrade to v2 or v3.