Reduce DB load upon initial connection due to channel loading (#12500)

#### Lazily loading channels

I've added a new RPC message called `SubscribeToChannels` that the
client now sends when it first renders the channels panel. This causes
the server to load the channels for that client and send updates to that
client as channels are updated. Previously, the server did this upon
connection.

For backwards compatibility, the server will inspect clients' version,
and continue to do this work immediately for old clients.

#### Optimizations

Running collab locally, I realized that upon connecting, we were running
two concurrent transactions that *both* queried the `channel_members`
table: one for loading your channels, and one for loading your channel
invites. I've combined these into one query. In addition, we now use a
join to load channels + members, as opposed to two separate queries.
Even though `where id in` is efficient, it adds an extra round trip to
the database, keeping the transaction open for slightly longer.

Release Notes:

- N/A

crates/rpc/proto/zed.proto

@@ -159,6 +159,7 @@ message Envelope {
         SetChannelMemberRole set_channel_member_role = 123;
         RenameChannel rename_channel = 124;
         RenameChannelResponse rename_channel_response = 125;
+        SubscribeToChannels subscribe_to_channels = 207; // current max
 
         JoinChannelBuffer join_channel_buffer = 126;
         JoinChannelBufferResponse join_channel_buffer_response = 127;
@@ -250,7 +251,7 @@ message Envelope {
         TaskContextForLocation task_context_for_location = 203;
         TaskContext task_context = 204;
         TaskTemplatesResponse task_templates_response = 205;
-        TaskTemplates task_templates = 206; // Current max
+        TaskTemplates task_templates = 206;
     }
 
     reserved 158 to 161;
@@ -1297,6 +1298,8 @@ message ChannelMember {
     }
 }
 
+message SubscribeToChannels {}
+
 message CreateChannel {
     string name = 1;
     optional uint64 parent_id = 2;

crates/rpc/src/proto.rs

@@ -277,6 +277,7 @@ messages!(
     (ShareProjectResponse, Foreground),
     (ShowContacts, Foreground),
     (StartLanguageServer, Foreground),
+    (SubscribeToChannels, Foreground),
     (SynchronizeBuffers, Foreground),
     (SynchronizeBuffersResponse, Foreground),
     (TaskContextForLocation, Background),