Multi-value type ahead custom fields

[#1]

As type-ahead fields are possible for certain types (e.g. users) we would need an option for multi-value fields here as well.

E.g. if we define a project team setup in a custom for, we are not able to assign multiple users to one role.

[#2]

We also have a few use cases for multi-select Type Ahead fields.  For User Type objects we would love to be able to use type aheads to list out Key Stakeholders or SMEs that can relate to a project or Request.