Description of problem:

When creating or editing a migration wave, the stakeholder groups field label is singular. 

Since the field supports multiple values, it should be plural, as stated in the enhancement description.

Version-Release number of selected component (if applicable): upstream

Steps to Reproduce:
1. Go to Migration -> Migration waves and click on "Create"

Actual results:

The stakeholder groups field label is singular.

Expected results:

The label should be plural.

Additional info: