This pull request adds a field import_dir to aqua.yaml, and it also adds command line options -u and -i to aqua init command.

e.g. aqua.yaml

registries:
- type: standard
  ref: v4.311.0
import_dir: imports

aqua init -u # Create aqua.yaml with `import_dir: imports`
aqua init -i pkgs # Create aqua.yaml with `import_dir: pkgs`

You can use import_dir and packages at the same time.
In addition to packages, aqua searches packages from the directory specified with import_dir.

import_dir: imports is equivalent to the following settings.

packages:
- import: imports/*.yml
- import: imports/*.yaml

And if import_dir is set, aqua g -i command creates a directory <import_dir> and adds packages to the file <import_dir>/<command name>.yaml.
For instance, if import_dir is imports, aqua g -i cli/cli creates a directory imports and adds cli/cli to imports/gh.yaml.

If the package has multiple commands, <command name> is the first command name in the files setting.
For instance, in case of FiloSottile/age, <command name> is age.

https://github.com/aquaproj/aqua-registry/blob/d39d4b5d0fb0635f6be7a70f3cb8b994f075a639/pkgs/FiloSottile/age/registry.yaml#L13-L17

    files:
      - name: age
        src: age/age
      - name: age-keygen
        src: age/age-keygen