This commit does the following:
- Splits the podman-systemd.unit.5.md into multiple files - one for each quadlet file type.
- Adds the podman-quadlet-basic-usage.7.md for quadlet examples.
- Majority of the text in the new files is copied from the podman-systemd.unit.5.md
- Adds support for very simple condditional in the markdown_preprocess.
- Uses new logic in markdown_preprocess in options/*.md to use a single .md file for both
podman subcommands man-pages and quadlet man-pages. This deduplicates the Quadlet man-pages a lot.
- Adds new `@@option quadlet:source.md`` preprocess command to import such .md files from options directory.
Signed-off-by: Jan Kaluza <jkaluza@redhat.com>
