REGTESTS: filters: Add a test for per-proxy stream filter ordering

REGTESTS: filters: Add a test for per-proxy stream filter ordering

Add a Lua filter exposing the attach order with a per-proxy ordinal and
the request/response evaluation order in a header. The reg-test checks
that instance-mode filters are attached in the global order and linked
to the request and response channels in their own order, that disabled,
declined and non-HTX filters are skipped, and that the legacy or
instance model is selected independently for each proxy, including
mix-and-match frontends and backends, and a listen proxy.