Shopify settings_schema fixes

[muchisx]

Hi!
Tested this on the tests folder.
What I managed with this

1) Validate that the root schema is an Array of atleast 2 items (theme metadata, and a settings_group)

2) Allow settings_group to be repeatable and correctly validated as a settings_group, benefiting from checks and snippets.

3) Validate that there's either theme_support_url or theme_support_email in the schema (following Shopify's docs).

4) A lot of individual validations for input-settings types.

This should set up the grounds for the settings_schema to be correctly validated,
next up, gotta add more snippets and make sure all info is updated with Shopify Docs

[panoply]

@muchisx can I merge this?

[muchisx]

hey @panoply its technically mergeable (it's functional now) but not complete in terms of there's content still left to be added for settings_schema