Spring Security SAML metadata Content-Type should be application/samlmetadata+xml

Expected Behavior The IANA-registered MIME type for SAML metadata is application/samlmetadata+xml.

Current Behavior The Saml2MetadataFilter responds with Content-Type: application/xml.

Context Not a big deal for human users looking to save and/or copy-paste the data, but automated tools may care, and standards should be followed where possible.