cephadm: bootstrap: verify orch module is running before setting cephadm backend

cephadm: bootstrap: verify orch module is running before setting cephadm backend

There have been occasional failures when bootstrapping with error
messages like

```
Module 'orchestrator' is not enabled/loaded (required by command 'orch set backend'): use `ceph mgr module enable orchestrator` to enable it
```

despite the orchestrator being meant to be an always on module.

Since trying to enable an already enabled module causes no issues,
trying to enable it ourselves seems like a sensible workaround.

Fixes: https://tracker.ceph.com/issues/67969
Signed-off-by: Adam King <adking@redhat.com>