h2c (cleartext HTTP/2) protocol support

[jpeach]

Based on the Listener definitions in #193, it's not all that clear how implementations should spec upgrading HTTP/1.1 to h2c.

This could be a property of the listener, but there's currently not a place for protocol-specific control fields. Otherwise, iit could be a property of the HTTPRoute, but that portion of the API is currently protocol-independent.

[fejta-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

[robscott]

/remove-lifecycle stale

[fejta-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

[fejta-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle rotten

[hbagdi]

/remove-lifecycle rotten
/lifecycle frozen

[jpeach]

Closing in favor of #817