refactor: clean up the logs and reduce noise

- Remove "Detected Autocrypt-mime message" logs printed for every incoming Autocrypt message.
- Print only a single line at the beginning of receive_imf with both the Message-ID and seen flag.
- Print Securejoin step only once, inside handle_securejoin_handshake or observe_securejoin_on_other_device.
- Do not log "Not creating ad-hoc group" every time ad-hoc group is not created, log when it is created instead.
- Log ID of the chat where Autocrypt-Gossip for all members is received.
- Do not print "Secure-join requested." for {vg,vc}-request, we already log the step.
- Remove ">>>>>>>>>>>>>>>>>>>>>>>>>" noise from securejoin logs.

src/securejoin/bobstate.rs

@@ -291,7 +291,7 @@ impl BobState {
     ) -> Result<Option<BobHandshakeStage>> {
         info!(
             context,
-            "Bob Step 4 - handling vc-auth-require/vg-auth-required message"
+            "Bob Step 4 - handling {{vc,vg}}-auth-required message."
         );
         if !encrypted_and_signed(context, mime_message, Some(self.invite.fingerprint())) {
             let reason = if mime_message.was_encrypted() {
@@ -333,7 +333,7 @@ impl BobState {
     ) -> Result<Option<BobHandshakeStage>> {
         info!(
             context,
-            "Bob Step 7 - handling vc-contact-confirm/vg-member-added message"
+            "Bob Step 7 - handling vc-contact-confirm/vg-member-added message."
         );
         mark_peer_as_verified(
             context,