Extension - Use connection pool for HTTP2 router connections

[huntharo]

Motivations

• Pertains to:
  • Cases where there is a single or few routers
  • Cases where there are very fast requests
• Saves 2-4 ms on very short requests by re-using an existing connection to the router when the next Lambda invoke asks to connect back to the same router

Acceptance Criteria

• Accomplish all of the below using the Hyper Client with connection pool
  • Keep info about which Router IP the connection is to
  • Keep info on when the connection was last used
  • Do not try to reuse the connection if 60 seconds or more have passed
  • If the initial request on the reused connection fails, establish a new connection instead
• Ensure that no delay remains enabled
• Ensure that TLS with invalid certs and non-TLS remain supported
• Add some TLS tests for router channels
• Review FIXME comments related to exiting a channel on a single error