Title: Access log command operator for HTTP request size including headers

Description:
Add a way to include the full size of a HTTP request, including headers, in access log entries.

Currently the command operators %BYTES_SENT% and %BYTES_RECEIVED% render the size of HTTP body, excluding headers. Add new command operators or specifiers for the existing ones to render the size of a HTTP request or response including:

• request line / status line
• headers
• body
• trailers

Relevant Links:

• (https://www.envoyproxy.io/docs/envoy/latest/configuration/observability/access_log/usage#command-operators)