Migrate v1 from gRPC to REST

[emgrav]

The v2 and v3 APIs are not feature complete, we are f.x. missing updating user metadata. We will need to keep using some v1 endpoints, so we should support these endpoints via the REST transport as well.

[sirewix]

Originally posted by @tlater-famedly in https://github.com/famedly/zitadel-actions-manager/issues/3:

Originally we envisioned the v2 API as replacing the v1 api entirely, and as such we left the v1 methods primarily as deprecated for backwards compatibility.

In practice, Zitadel's v2 API should be seen as an extension of the v1 API, so this doesn't really work.

We have decided to provide the same clients for "both" APIs, and generate our own types to use it instead of using the upstream zitadel crate. This will allow us to actually deprecate the "v1" API, and make it easier to provide as-yet unimplemented methods for the "v1" API.

[sirewix]

This is possibly done already. AFAIK we don't use v1 client anywhere (except maybe some old repos and test suites). So we need to:

• Go through all actively maintained repos and see if v1 client is still used somewhere.
• Add any missing methods to v2 (that we need)
• Mark v1 client as deprecated
• Remove it from the set of default features
• Delete it completely??