jinja2 templates in snow DA

[aerorahul]

This PR:

• updates the snowDA yamls to jinja2 templates removing all $( ) and ${ } template forms.
• all inclusion is now performed via jinja2 include with the appropriate indentation.
• jinja2 templates for yamls now carry a .j2 extension to identify them as templates.
• requires feature/jinja2_includes branch from wxflow.

parse_j2yaml from wxflow now does not render the $( ) templates. This change is not backwards compatible.

Corressponding PRs in wxflow and global-workflow are:

• Enable searching for included templates when rendering jinja2 templates. wxflow#15
• Reformat snowDA templates to jinja2 global-workflow#2371

[CoryMartin-NOAA]

Very minor comment, but this looks great, thanks for doing this!