MCP: Use Databricks SDK to authenticate SQL calls (#3949)

## Changes

This way we don't have to rely on PAT anymore. 

## Why
<!-- Why are these changes needed? Provide the context that the reviewer
might be missing.
For example, were there any decisions behind the change that are not
reflected in the code itself? -->

## Tests

Created an app through the agent and validated that it works without
configuring a PAT.

Author: fjakobs

experimental/apps-mcp/lib/templates/trpc/package.json

@@ -5,6 +5,7 @@
     "install:all": "cd server && npm install && cd ../client && npm install",
     "build": "npm run install:all && cd server && npm run check && cd .. && cd client && npm run build && cd .. && rm -rf server/public && mv client/dist server/public",
     "start": "cd server && npm start",
-    "test": "cd server && npm test"
+    "test": "cd server && npm test",
+    "clean": "rm -rf server/public server/node_modules client/node_modules"
   }
 }