Conversation Tag - Allow attaching tags to conversations

Allow adding multiple tags to conversations and then filtering conversations by tags.

Example scenario

When new lead is being converted to a more potential customer, then tagging it accordingly (i.e. Potential Customer tag) would simplify the customer support & sales management.

In addition, when a customer has revealed their requirement, then a possible plan tier tag can also be added - hence simplifying the handover to a customer success personal.