collab: Use the right zed.dev URL for the environment (#15566)

This PR updates collab to pick the `zed.dev` URL based on the current
environment rather than always using `https://zed.dev`.

This means that when developing locally we'll use
`http://localhost:3000` to be taken to the locally-running version of
`zed.dev`.

Release Notes:

- N/A

crates/collab/src/lib.rs

@@ -163,6 +163,15 @@ impl Config {
     pub fn is_development(&self) -> bool {
         self.zed_environment == "development".into()
     }
+
+    /// Returns the base `zed.dev` URL.
+    pub fn zed_dot_dev_url(&self) -> &str {
+        match self.zed_environment.as_ref() {
+            "development" => "http://localhost:3000",
+            "staging" => "https://staging.zed.dev",
+            _ => "https://zed.dev",
+        }
+    }
 }
 
 pub struct AppState {