Due to creating a context with a timeout prior to blocking on the
session channel to wait for it to end, the timeout of the context will
likely already hvae expired by the time the kvstore operation is
performed. It is thus cancelled immediately, requiring a subsequent
controller call. This prolongs the time the session is renewed and
causes unnecessary controller failures which can be mistaken for etcd
issues.

Also pass the etcd client context to the controller to bind the
lifecycle of a controller run to it.

This fixes errors like these:
```
  kvstore-etcd-lock-session-renew   20s ago        10s ago      1       unable to renew etcd lock session: context deadline exceeded
```

Signed-off-by: Thomas Graf <thomas@cilium.io>