Auto create app if not exist

[kodless]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature

What is the current behavior? (You can also link to an open issue here)

After starting leek, developers need to open Leek UI in browser and manually create the app to match the one in agent subscriptions. until then the agent will keep showing this warning:

leek-app-1        | WARNING:leek.agent.consumer:(main) b'{"error": {"code": "404001", "message": "Application does not exist", "reason": "Index not yet created, use Leek UI to create a new application"}}\n'

What is the new behavior (if this is a feature change)?

Leek agent will auto-create the application if environment variable LEEK_CREATE_APP_IF_NOT_EXIST is set to true.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No