Manage start command in envd

[ValentaTomas]

Right now the start cmd is managed by systemd. This PR changed it so it is managed by envd which allows us better control over it and also allows integration with logging.

Tasks

• [ ] Handle/communicate that the start cmd will be started during build without internet now
• [x] Modify old start cmd log handlers in SDKs
• [x] Permissions bug - use root for the start command
• [x] Fix start cmd not starting jupyter server (waiting...)

[ValentaTomas]

We may want to rethink the proper way to handle start command — even when we move the management to envd there are questions about storing start command logs and how to handle output subscriptions/reconnecting.

[jakubno]

Jupyter + info about starting the sandbox are exported

[ValentaTomas]

Jupyter + info about starting the sandbox are exported

What is the format of results/stdout/stderr from the jupyter in the logs?