Use Enum instead of string / number values

[ssomnath]

For things like dependency types, consider using Enum instead of manually changing the mode to 0, 1, 2, etc.

[dvstans]

This ticket is too vague to be actionable. Please re-write as separate tickets for specific instances where enums should be used. Protobuf already defines enums when needed; however, dependency type is a special case and cannot be an enum as it needs to be expandable (a short string referencing an relationship definition).

[dvstans]

This isn't really actionable. Closing.