Merge the BSL and sync controllers

[carlisia]

The BSL and sync controllers both do (different) operations that depend on connecting to the object store. By merging these controllers the number of connections to the store would greatly reduce (which is good for rate limiting) and having one less controller to maintain would not be bad either.

Pre-requisite: convert the sync controller to the controller-runtime library (see Modernize the Velero code base · Issue #2597 · vmware-tanzu/velero)

Related: Improve BSL controller performance · Issue #2883 · vmware-tanzu/velero