Support LambdaLabs backend in UI

[r4victor]

LambdaLabs backend is already implemented on the server side (#508). We need to support LambdaLabs in the UI.

The configuration page should include:

1. API Key
2. Regions (Multiselect. We support configuring multiple regions for lambda)
3. Storage type (we support only aws for now)
4. Storage config:
   1. AWS secret/access key
   2. AWS bucket