[HTTP] Audit implementation of upstream connections

[yanavlasov]

Audit implementation of upstream connections for potential problems with untrusted upstream servers

There are several areas that needs to be verified and audited. Specifically:

• Reuse of connection to H/1 upstream servers. Presently connection is reused very quickly and this may pose a problem with servers that respond twice. TBD: define the end goal. Protecting Envoy? Flagging misbehaving upstream servers?
• Verify that idle timeouts for upstream connections work.
• Code for retrying requests to upstream servers.
• Audit handling of trailers.

Sub-task of #12278

[stale]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or other activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed because it has not had activity in the last 37 days. If this issue is still valid, please ping a maintainer and ask them to label it as "help wanted". Thank you for your contributions.