Centralize ZED_STATELESS (#37492)

Closes #ISSUE

Centralizes the references to the `ZED_STATELESS` env var into a single
location in a new crate named `zed_env_vars`

Release Notes:

- N/A *or* Added/Fixed/Improved ...

script/new-crate

@@ -63,6 +63,7 @@ anyhow.workspace = true
 gpui.workspace = true
 ui.workspace = true
 util.workspace = true
+workspace-hack.workspace = true
 
 # Uncomment other workspace dependencies as needed
 # assistant.workspace = true