Create User Tags and Segments

Similar to Email Marketing software, add a user tag API.

Use builtin tags for access plans, memberships, courses, etc and other properties to create builtin segments and allow users to create custom segments. Mailchimps Segmentation is a great research point: https://mailchimp.com/help/all-the-segmenting-options/ and https://mailchimp.com/features/advanced-segmentation/

Segments can be a great basis for creating variations in course pathways and experiences #522

Segments (and/or tags) can be a quick & direct way to check permissions and access to course elements.

Segments can also be a basis for engagements.

Segments can work to customise the Merge Codes available in a context #560