listener: add envoy internal listener

[lambdai]

Commit Message:
The internal listener at connection handler setting register itself on certain internal address.
This PR demonstrate how an internal listener register on the dispatcher, and the flow of
dispatcher could create a internal connection pair when the cluster wants to connect to
the internal listener.

Also rename the Network::ListenerImpl to Network::TcpListenerImpl

Additional Description:
The internal connection is not implemented yet. The next PR will provide the implementation
of user space connection.
Extracted from https://github.com/lambdai/envoy-dai/tree/wiphostconn
on top of #12837 as how internal server address is used

Part of #11725

Risk Level:
Testing:
Docs Changes:
Release Notes:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Deprecated:]

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to api/envoy/.
CC @envoyproxy/api-watchers: FYI only for changes made to api/envoy/.

🐱

Caused by: #12838 was opened by lambdai.

see: more, trace.

[lambdai]

New internal listener type

[alyssawilk]

Want to ping back on this one once CI is happy, or let me know why CI failures are to be expected?

[htuch]

CC @penguingao re: layering, composition of filters and internal loopback.

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in 7 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically closed because it has not had activity in the last 37 days. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!