Wait until cluster is ready before adding to MC-query client + move client creation out of middleware

[foot]

• (The main fix): Bring in changes from core Move kube Client creation into the handlers and out of the middleware weave-gitops#2252 that moves client out of middleware, so routes that don't use the MC-querier (like /v1/clusters), will still work even if there is an issue w/ the MC-querier
• Check for Ready before adding GitopsCluster to the MC-querier:
  • To stop the querier from trying to connect to non-Ready clusters and bringing down the whole system.
  • Make the system a bit easier to reason about, if GitopCluster is not ready we're not querying it.
  • Potentially this will add another (worst case ~29s) before the cluster begins to be queried
• Refactor tests a bit as we have to pass through clientsFactory everywhere

Fixes #806
Fixes #829
Fixes #828

[foot]

Still receive errors with this which is strange:

{"code":2,"message":"error getting clusters: etcdserver: request timed out","details":[]}

Might be something as the CP comes up.

[alichaddad]

LGTM

[sarataha]

Perfect! 🙂 🥇