Api session id support (#2158)

* Refactor api endpoint chat handler to its own function
remove legacy `chatWithWorkspace` and cleanup `index.js`

* Add `sessionId` in dev API to partition chats logically statelessly

server/endpoints/workspaceThreads.js

@@ -138,6 +138,7 @@ function workspaceThreadEndpoints(app) {
             workspaceId: workspace.id,
             user_id: user?.id || null,
             thread_id: thread.id,
+            api_session_id: null, // Do not include API session chats.
             include: true,
           },
           null,