Add a CI step to run SFR specific specs

With the addition of #15 we need a way to run some liquid specs in the context of storefront-renderer. I think adding a CI step to execute these tests in SFR would be the ideal way forward.

Storefront Renderer Challenges

We don't have access to the Liquid filters, tags, or drops defined in storefront renderer. So running the tests in this repo is challenging. I may end up getting these types of specs to run in storefront-renderer itself or setting up a build container on this repo that will run them with the SFR code.

Missing Storefront Liquid Features

# Tag
Liquid::Template.register_tag('layout', Layout)
Liquid::Template.register_tag('form', FormTag)
Liquid::Template.register_tag('paginate', PaginateTag)
Liquid::Template.register_tag('style', StyleTag)
Liquid::Template.register_tag('render', RenderTag)
Liquid::Template.register_tag('javascript', SectionAndBlock::JavaScriptTag)
Liquid::Template.register_tag('schema', SectionAndBlock::SchemaTag)
Liquid::Template.register_tag('stylesheet', SectionAndBlock::StyleSheetTag)
Liquid::Template.register_tag('section', SectionAndBlock::SectionTag)

# Filters
Liquid::Template.register_filter(FormFilter)
Liquid::Template.register_filter(I18nFilter)
Liquid::Template.register_filter(UrlFilter)
Liquid::Template.register_filter(JsonFilter)
Liquid::Template.register_filter(ColorFilter)
Liquid::Template.register_filter(MoneyFilter)
Liquid::Template.register_filter(StringFilter)
Liquid::Template.register_filter(CollectionFilter)
Liquid::Template.register_filter(TagFilter)
Liquid::Template.register_filter(CryptoFilter)
Liquid::Template.register_filter(CustomerAccountFilter)
Liquid::Template.register_filter(CurrencyFormFilter)
Liquid::Template.register_filter(PaginationFilter)
Liquid::Template.register_filter(WeightFilter)
Liquid::Template.register_filter(TextFilter)
Liquid::Template.register_filter(FontFilter)
Liquid::Template.register_filter(DistanceFilter)
Liquid::Template.register_filter(MediaFilter)
Liquid::Template.register_filter(ThemeFilter)
Liquid::Template.register_filter(MetafieldFilter)

Start by reviewing issue #15 and the Storefront Renderer context described here, then determine where the SFR-specific Liquid specs should execute. Use the listed missing tags and filters to define the required test environment; done means CI runs these specs with the Storefront Renderer features available.