GEP-2643: TLSRoute (#4064)

* GEP-2643: TLSRoute

* Add multiplexing to TLSRoute

* Update TLSRoute GEP with more information

* Add support for TLSRoute termination

* Fix some comment reviews

* Move multiplexing to its own GEP

* Fix gatewayapi reviews

* Fix some more reviews

* Fixes on some wording

* Add reference to other GEPs

* Add conformance for non supported termination

* Add conformance, fix mixed mode, fix metadata

* Be explicit on conformance intent for failed listener

* Add conformance issues and codes to conformance table

* Address comments on GEP

* address comment reviews, add tlsmode validation

* Apply suggestions from code review

Co-authored-by: Nick Young <[email protected]>

* Fix feature names on TLSRoute gep

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Co-authored-by: Nick Young <[email protected]>

Author: rikatz