[FEATURE REQ] Define and implement general guidelines on handling terminal subscribe() calls

Libraries, especially messaging, have several subscribe() calls in the state machine. Sometimes, terminal errors from these calls are bypassed to the reactor's default onErrorDropped handlers, which increases noise in the error log levels.

Creating this issue to centralize handling of such subscribe() calls as @lmolkova pointed out [here](https://github.com/Azure/azure-sdk-for-java/pull/42804#discussion_r1829793273).