[airflow] add `airflow` CLI autocomplete

[prakshalj0512]

Sanity checks

• [X] My issue relates to a specific CLI completion spec (e.g. git checkout is missing options in git completion spec). If your issue is more general, please create your issue here: withfig/fig
• [X] I have searched github.com/withfig/autocomplete/issues and there are no duplicates of my issue
• [ ] I would like to work on this.

What CLI tool does this relate to?

airflow

Which statement makes the most sense?

This completion spec does not exist

Issue Details

missing specs for apache-airflow package

usage: airflow [-h] GROUP_OR_COMMAND ...

positional arguments: GROUP_OR_COMMAND

Groups:
  celery         Celery components
  config         View configuration
  connections    Manage connections
  dags           Manage DAGs
  db             Database operations
  jobs           Manage jobs
  kubernetes     Tools to help run the KubernetesExecutor
  pools          Manage pools
  providers      Display providers
  roles          Manage roles
  tasks          Manage tasks
  users          Manage users
  variables      Manage variables

Commands:
  cheat-sheet    Display cheat sheet
  info           Show information about current Airflow and environment
  kerberos       Start a kerberos ticket renewer
  plugins        Dump information about loaded plugins
  rotate-fernet-key
                 Rotate encrypted connection credentials and variables
  scheduler      Start a scheduler instance
  standalone     Run an all-in-one copy of Airflow
  sync-perm      Update permissions for existing roles and optionally DAGs
  triggerer      Start a triggerer instance
  version        Show the version
  webserver      Start a Airflow webserver instance

optional arguments: -h, --help show this help message and exit