Improve the SQL CLI documentation (YML)

[tatiana]

Currently, we have one page for getting started. However, we are missing separate documentation per feature.

We are missing structured documentation pages for all currently supported features:

• configuration.yml
  • connections (with examples for all currently supported providers)
  • other possible configuration options (e.g. airflow_home)
• workflows
  • what is a workflow
  • different kind of files (yaml, sql)
  • create dependencies via jinja templating syntax i.e. {{ }}
• sql files
  • a select statement
• yml files
  • load_file (all possible parameters or link to astro-sdk docs)

[feluelle]

I have added some points I find important to cover. Feel free to edit.