Add an --edge option to the new management command

[ellmetha]

Description

Let's make it possible to generate new projects (or applications) that use the development version of Marten through the use of an --edge / -e option. When this option is set, the generated project structure should include a shard.override.yml file (in addition to the shard.yml file) with the following content:

dependencies:
  marten:
    github: martenframework/marten
    branch: main

This will ensure that the project uses the development version of Marten (main branch) when running the shards install command (ref).

[notramo]

I would recommend --nightly, or --dev-preview as those seem less ambigous.