Add support for MSC4155 (#1013)

[rendered msc here](https://github.com/Johennes/matrix-spec-proposals/blob/johannes/invite-filtering/proposals/4155-invite-filtering.md). Closes #836.

Co-authored-by: nexy7574 <git@nexy7574.co.uk>
Reviewed-on: https://forgejo.ellis.link/continuwuation/continuwuity/pulls/1013
Reviewed-by: nex <nex@noreply.forgejo.ellis.link>
Co-authored-by: Ginger <ginger@gingershaped.computer>
Co-committed-by: Ginger <ginger@gingershaped.computer>

src/database/maps.rs

@@ -434,4 +434,8 @@ pub(super) static MAPS: &[Descriptor] = &[
 		name: "userroomid_notificationcount",
 		..descriptor::RANDOM
 	},
+	Descriptor {
+		name: "userroomid_invitesender",
+		..descriptor::RANDOM_SMALL
+	},
 ];