Entity already exists support for topic subscription (Legacy)

Adds

• Add support for Topic subscription for Legacy project to manage existing entities
  • When active subscriber is changes e.g. on network failure, support internally the subscriber change, and manage possible exsisting subscription from the previous client having these network or other problems
  • One scenario could be two subscribers where A is active and B passive. A has network or server failure, and traffic is moved to B. B is now active and A passive. B will subscribe to same messages as A was. This can cause EntityAlreadyExsists -type exceptions on certain cases. Handle these internally.
  • Now client can optionally implement Delete Subscription -logic when creating message subscriber - but is no longer necessary