The %UPSTREAM_CLUSTER% formatter is affected by alt_stat_name, but there are times where a custom stat name may have special delimeters meant to help with stat tag regex parsing but those delimeters shouldn't show up in access logs. In these cases, %RAW_UPSTREAM_CLUSTER% could be used.

Commit Message: Add %RAW_UPSTREAM_CLUSTER% access log formatter
Additional Description:
Risk Level: no
Testing: unit
Docs Changes:
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Request variables

Key	Value
ref	ef2c7d4
sha	3fca89c
pr	35265
base-sha	8a214e8
actor	@keithmattix
message	Add %UPSTREAM_CLUSTER_RAW% formatter...
started	1721795255.658214
target-branch	main
trusted	false

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