Enabling available subcommands when cli isn't installed

[anuunchin]

Description

The Available Subcommands for dlt deploy, including github-action and airflow-composer, are displayed in help even when the dlt[cli] extra is not installed.

Related Issues

• Doesn't directly fix, but is related to CLI does not recognize required arguments for dlt deploy command with github-action deployment method #2195

Additional Context

Basically, now the pipdeptree and cron_descriptor imports in deploy_command_helpers.py do not fail, and plugins.py directly checks if they can be available in order to decide whether the deploy_command_available resolves to True - instead of depending on a ModuleNotFound error that stems from these imports in deploy_command_helpers.py.

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[anuunchin]

For context, the subcommands are visible with dlt deploy -h even when the cli extension is not installed. So the result is:

anuunchinbat@anuuns-Air dlt % dlt deploy -h
Usage: dlt deploy [-h] pipeline-script-path {github-action,airflow-composer} ...

The dlt deploy command prepares your pipeline for deployment and gives you step-by-step instructions on how to accomplish it. To enable this functionality, please
first execute pip install "dlt[cli]" which will add additional packages to the current environment.

Positional Arguments:
  pipeline-script-path  Path to a pipeline script

Options:
  -h, --help            show this help message and exit

Available Subcommands:
  {github-action,airflow-composer}
    github-action       Deploys the pipeline to Github Actions
    airflow-composer    Deploys the pipeline to Airflow

Previously it was:

anuunchinbat@anuuns-Air dlt % dlt deploy -h
Usage: dlt deploy [-h] pipeline-script-path

The dlt deploy command prepares your pipeline for deployment and gives you step-by-step instructions on how to accomplish it. To enable this functionality, please
first execute pip install "dlt[cli]" which will add additional packages to the current environment.

Positional Arguments:
  pipeline-script-path  Path to a pipeline script

Options:
  -h, --help            show this help message and exit

[sh-rp]

lgtm!