Set default git settings

[lmakarov]

While docksal/cli support passing hosts git settings via GIT_USER_EMAIL and GIT_USER_NAME, often the host system would not have these configured, which may result in difficult to diagnose issues in non-interactive scenarios and scripts (e.g., acquia/blt#2971)

We should provide default values out of the box:

GIT_USER_EMAIL=${GIT_USER_EMAIL:-cli@docksal.io}
GIT_USER_NAME=${GIT_USER_NAME:-Docksal CLI}