Add "Relational Only" to permission levels

[benhaynes]

A common use-case is admins wanting to fetch relational data, but not wanting to open-up full read access to that related collection.

For example, you may want to return Project > Files (deep relational) but don't want to completely open up READ access to the directus_files collection.

So we could add a new permission level that only allows CRUD access when it's performed through a relationship. So we'd end up with:

• None
• Mine
• Role
• Relational
• Full

Keeping in mind that "mine" and "role" will eventually be combined into one "dynamic rules" option.

One issue with this is that inevitably admins will want to configure which relationships allow access (instead of turning this on globally). So a proper solution takes this into consideration.

[benhaynes]

To achieve better clarity/visibility, we are now tracking feature requests within the Feature Request project board.

This issue being closed does not mean it's not being considered.