Add "local mode" to support locally defined content in a Labspace

[mikesir87]

When a Labspace starts, it will, by default, clone the content from the content repo. However, there may be situations in which you want to skip this and use locally cloned content, such as running demos.

This PR provides the ability to configure the configurator service with a "local mode" option. In this scenario, there will be no remote git cloning. Instead, the content is mounted into the configurator and then copied into the content volume used in the Labspace.

Example Compose override

This override file will mount the parent directory into the Labspace and use it as the content source

services:
  configurator:
    volumes:
      - ../:/custom-content
    environment:
      LOCAL_MODE: "true"
      LOCAL_CONTENT_PATH: /custom-content