This PR repurposes the `--install` argument as a flag to disable download and installation of the Vegvisir git submodule.
A new flag `--dir` is used to specify the install directory instead of `--install`.
Reviewed-on: https://codeberg.org/vegvisir/install/pulls/6
I will remove generated envvars for optional parameters. Vegvisir will automatically fall back to its internal defaults if certain parameters are absent.
I had to leave `worker_magic_pathname` in for now thought since the Vegvisir default for that is incorrect. When [PR #60](https://codeberg.org/vegvisir/vegvisir/pulls/60) is merged into the Vegvisir master, I will remove it from here.
Reviewed-on: https://codeberg.org/vegvisir/install/pulls/4