Add honor_authnrequest_nameidpolicy_format boolean field to SAMLConfig.
The intended use is to enable honoring the nameid policy format requested
by the SP's AuthnRequest, on a config-by-config basis.
This is done because a change to fully support honoring this with
appropriate semantics is large and likely to break existing remotes, so this
allows a smaller change that works for specific remotes.
Merged from https://code.launchpad.net/~roadmr/canonical-identity-provider/honor-authnrequest-nameid-policy-format-field/+merge/361981