[DPE-3737] Implement ZK client interface

[Batalex]

The following changes were made to the interface:

• Replaced* chroot by database
• Replaced chroot-acl by extra-user-roles
• Replaced uris by endpoints

*well, not exactly "replaced", we kept the old fields around for backward compatibility.

There are a few issues with the charm-relation-interfaces repository:

• it needs two repositories to function, local tests can only be run against a remote repo, hence the use of my own fork that should be removed
• the two repositories need to use the same pydantic version. This is an issue because the interface schema defined in https://github.com/canonical/charm-relation-interfaces/pull/144 originally used v2, but data-platforms-libs require v1
• the relation now uses a chain of events to set the databag, which appears to be difficult (impossible?) to test with interface_tester