Add support to print %UPSTREAM_CONNECTION_ID% in access log. Currently, %CONNECTION_ID% is supported which prints downstream connection id in access log. Primary motivation for add this is to easily debug reuse of an existing connection while debugging communication between client -> server especially during draining of upstream envoy.

Commit Message: Add support for %UPSTREAM_CONNECTION_ID% in access log
Additional Description: Primary motivation for add this is to easily reason reuse of an existing connection while debugging communication between client -> server.
Risk Level: low
Testing: unit testing
Docs Changes: updated
Release Notes: updated

Request variables

Key	Value
ref	df375125f840d0a923c2bf3dde5d3bd31e583e96
sha	87cad0a
pr	31920
base-sha	6952f54
actor	@deveshkandpal1224
message	access log: add support for %UPSTREAM_CONNECTION_ID%...
started	1706065052.407297
target-branch	main
trusted	false

Container image/s (as used in this CI run)

Envoy version (as used in this CI run)