ContactAssociation make Role required

[gsnider2195]

Environment

• Nautobot version (Docker tag too if applicable): 2.2.0a1
• Python version:
• Database platform, version:
• Middleware(s):

Steps to Reproduce

1. Create a contact association to an object without selecting a role
2. Assign that same contact to the same object with the same status and no role

Expected Behavior

Failure because contact already exists on that object

Observed Behavior

Multiple associations are created because null != null on the role field

[gsnider2195]

As discussed, make role required

[glennmatthews]

Implemented in #5279.