Support for sending response body, headers, and status code to client on Extauthz filter CheckStatus::Error

[mikehuston]

Title: Support for sending response body, headers, and status code to client on Extauthz filter CheckStatus::Error

Description:
Allow both http and grpc extauthz filters to support sending response headers and status code from the extauthz service to the client on extauthz 5xx response. I'm looking for #24845, for both HTTP and gRPC extauthz filter impls.

What scenarios it enables:

• [Response headers] When our extauthz service returns 5xx, it'd be extremely useful for downtime debugging and error attribution to pass internal metadata about the errored request (such as token type used, customer identifier, high level error category) to our Envoy access logs (we will remove these internal headers before sending the response to the client).
• [Status code] clients can distinguish between 500 (internal error, don't retry) and 503 (temporarily unavailable, retry)
• [Body] a custom response body that contains a unique request identifier and/or error message will help customers and us determine next steps of action for errored requests.
• [Response headers] It will allow us to send headers to the client such as Retry-After for 503

Relevant Links:
#24845

[phlax]

cc @agrawroh @esmet @tyxia @ggreenway

[github-actions]

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 "no stalebot" or other activity occurs. Thank you for your contributions.

[github-actions]

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" or "no stalebot". Thank you for your contributions.