Consolidate TargetRef validation logic for Policy CRD's

[mikhail-aws]

We have multiple CRD that use Policy Attachment: AccessLog, AuthPolicy, TargetGroupPolicy, VpcAssociationPolicy.

All of above preform similar validation on TargetRef:

• GroupName and Kind
• Namespace
• Conflict with other Policies
• TargetRef is not found

Currently each policy has own "flavor" of doing it, but essentially it's same logic with different types.