Calculate status phase based on status conditions

With #302 (closed) we now have status conditions in addition to the existing status phase. In order for phase to remain accurate, we should set phase based on status conditions. This will involve removing the phase set calls from https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/blob/master/controllers/gitlab_status.go and instead setting phase based on the status conditions.

Proposed logic:

• Phase is set to "Running" only when conditions Initialized = True, Available = True, Upgrading = False
• Otherwise Phase is set to "Preparing"

We will expand/fix the Phase vocabulary in #316 (closed). For this issue we can stick with "Running" and "Preparing".