Add pluggable C2 transport mechanism to metasploit

[adfoster-r7]

Placeholder ticket, nothing actionable here - with no plans to implement it currently. Just creating a dedicated Github issue for this for tracking purposes

Related to the Github discussion: #14490

A lot of post exploit frameworks have a pluggable mechanism for C2 transport evasion.

Meterpreter Transport and Scalability Overhaul
The Meterpreter Protocol “TLV” is enhanced to support modern features such as logging, unidirectional messages, obfuscation, sequence number reassembly and more. This feature will enable Meterpreter sessions to be more robust, faster, and evade detection with greater ease than before.

Additionally, Meterpreter payload listeners, rather than being integrated straight into msfconsole, will run as an independent process that communicates with msfconsole (1 or more users) over RPC similar to the msfdb_ws (Metasploit Database Web Service). The external listener then replaces the ‘metasploit-aggregator’ project by not requiring an intermediate proxy to park or share sessions, these are done directly by having the listeners independent of console users.

Listener capabilities be embeddable directly into Meterpreter payloads, allowing local listeners and remote listeners internal to other networks could be implemented the same way, enabling greater scalability and facilitating pivoting across more complex networks, allowing better post-exploitation possibilities in modern network environments.

Integration with external C2 frameworks
If listeners are externalized, then there is an API layer both for interactive interaction with remote sessions, and a way for the Post-exploitation API to communicate with the external sessions. That should mean that if an external C2 framework supports at minimum shell interaction, a bulk of the Post-exploitation API should be applicable against external C2 frameworks as well. Metasploit would then be able to integrate both with other open-source C2 frameworks, as well as private ones.

https://docs.metasploit.com/docs/development/propsals/msf6-feature-proposals.html#payloads-and-post-exploitation