Wire up UI for requesting contacts and cancelling requests

Co-Authored-By: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/rpc/src/proto.rs

@@ -82,6 +82,7 @@ messages!(
     (ApplyCompletionAdditionalEditsResponse, Background),
     (BufferReloaded, Foreground),
     (BufferSaved, Foreground),
+    (RemoveContact, Foreground),
     (ChannelMessageSent, Foreground),
     (CreateProjectEntry, Foreground),
     (DeleteProjectEntry, Foreground),
@@ -188,6 +189,7 @@ request_messages!(
     (RegisterWorktree, Ack),
     (ReloadBuffers, ReloadBuffersResponse),
     (RequestContact, Ack),
+    (RemoveContact, Ack),
     (RespondToContactRequest, Ack),
     (RenameProjectEntry, ProjectEntryResponse),
     (SaveBuffer, BufferSaved),