Match a consumer to an identity source user

Binds the consumer to a user of an identity source of the project, by the source's name (sourceType ldap, database or api, any other is 400; sourceName; username = the key the next sync reconciles on; optional email, fullName, ldapDn). The consumer becomes sync-managed: the source owns its identity fields from then on. An unknown source is 404; a source whose synchronization is disabled is 400 (reason syncProviderDisabled); a username another consumer holds is 400 (reason credentialUsernameTaken). The same step the Consumer screen's match flow runs; runtimeDeployment reports the gateway push.