[Docs - New Feature]: shallow cloning

[akosyakov]

Describe your feature

We should clarify that we do shallow clone during workspace startup and unshallow in the background in regular runnig workspace.

How to test

See https://github.com/gitpod-io/gitpod/issues/6796

[fmartins]

Have you considered adding a system property that allows disabling the unshallow background task?

[Siddhant-K-code]

@loujaybee Any Plans for this?