Configure Envoy to validate client certificates, using the union of all
relevant client CA bundles (that is, a bundle of the main client CA
setting together with all per-route client CAs). Pass the validation
status from Envoy through to the authorize service, by configuring Envoy
to use the newly-added SetClientCertificateMetadata filter, and by also
adding the relevant metadata namespace to the ExtAuthz configuration.
Remove the existing 'include_peer_certificate' setting from the ExtAuthz
configuration, as the metadata from the Lua filter will include the full
certificate chain (when it validates successfully by Envoy).
Update policy evaluation to consider the validation status from Envoy,
in addition to its own certificate chain validation. (Policy evaluation
cannot rely solely on the Envoy validation status while we still support
the per-route client CA setting.)
