Let an operator set both HTTP/2 bridge admission caps through
PAPERCLIP_MAX_PARALLEL_HTTP2_BRIDGE_REQUESTS and
PAPERCLIP_MAX_LIVE_HTTP2_BRIDGE_SESSIONS. The new env helper runs each
per-field resolver with a bound reporter before the joint budget check, so a
per-field rejection is never silent. The host logs a refused cap pair at
error level with the refused total and the reserved budget, and never keeps
one operator value and one default from a refused pair.
Co-authored-by: Paperclip <noreply@paperclip.ing>