Add controller for TargetAllocator CR

[swiatekm]

Description:

Add the controller for the TargetAllocator CRD. This is just the controller code with unit tests, it is not actually enabled and there's no user-facing impact.

Some associated changes include:

• The Collector in TargetAllocator manifest generation parameters becomes optional. This is necessary because we need to be able to reconcile a TargetAllocator without a collector. This, in effect, starts a Target Allocator which doesn't allocate targets anywhere, but still computes them.
• There's some associated changes to TA ConfigMap generation enabling the above.

Link to tracking Issue(s): #2422

Testing:

Documentation:

[swiatekm]

I'm planning to add more tests for this, but what's already here is reviewable as-is.