Replace POST /worktrees rest endpoint with GET /rpc-address

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

zed-rpc/src/rest.rs

@@ -1,7 +1,8 @@
 use serde::{Deserialize, Serialize};
 
 #[derive(Serialize, Deserialize)]
-pub struct CreateWorktreeResponse {
-    pub worktree_id: i32,
-    pub rpc_address: String,
+pub struct GetRpcAddressResponse {
+    pub address: String,
 }
+
+pub const GET_RPC_ADDRESS_PATH: &'static str = "/api/rpc-address";