Allow internal manual batching for declarations

[Mallets]

Describe the feature

Certain declarations like declare_subscriber, declare_publisher, etc. trigger multiple declaration messages being sent over the network. Automatic batching relies on the network back pressure, a manual mechanism could be introduced internal for declarations.

[jcos1]

Minimizing declaration messages looks somewhat related to predefining declarations in the config suggested here: eclipse-zenoh/roadmap/discussions/181