Enhance EnrollmentFlow model with field to indicate it is a pathway that can only be done in-person

[angela-tran]

We need a way to represent that a flow is digital-only, in-person only, or supports both.

Acceptance Criteria

• A flow that is digital-only shows up only on the digital side
• A flow that is in-person only shows up only on the in-person side
• A flow that supports both shows up on both sides

[angela-tran]

ignore this comment 😅

Done shaping, need to ask for feedback

My thought on this is that this modeling reflects the use case we have in mind. We can refactor this field into something else if the use case changes.

[thekaveman]

Let's align the field naming here with what we choose for the property name in #2245

@indexing suggests supported_methods for the name of the field/property.

Devs suggest possible values of digital or in_person. Note this should be a multi-select: one or both values can be chosen.

[thekaveman]

This can reuse some of the helpers introduced in #2367

E.g. benefits.core.models.EnrollmentMethods is a class with two properties for the strings digital and in_person.