text: Title: [Dev] Automatically source the sky environment for dev mode
  Body: <!-- Describe the bug report / feature request here -->
  
  It is a little bit tedious to manually `source ~/skypilot-runtime/bin/activate` for dev on sky serve/managed jobs. Can we support automatically activate it for dev mode (e.g. `SKYPILOT_DEV=1`)?
  
  
  <!-- If relevant, fill in versioning info to help us troubleshoot -->
  _Version & Commit info:_
  * `sky -v`: PLEASE_FILL_IN
  * `sky -c`: PLEASE_FILL_IN
  