Unspecced `org.matrix.cross_signing_reset` UIA type
Element-web appears to have special handling for an unspecced org.matrix.cross_signing_reset user-interactive auth type.
Support for unspecced APIs makes debugging difficult, because we don't know what it's supposed to do.
This is a MAS-Synapse special which should have been MSC'd but looks like it missed the boat https://github.com/element-hq/synapse/pull/17509#issuecomment-2298287246
Also supported by matrix-rust-sdk https://matrix-org.github.io/matrix-rust-sdk/src/matrix_sdk/encryption/mod.rs.html#363-378
apparently this is https://github.com/matrix-org/matrix-spec-proposals/pull/4312