Handle is_num_identity_overrides_complete field in the feature list UI

[matthewelwell]

The backend has added a new is_num_identity_overrides_complete to each feature when retrieving the list of features for a given project (and when the environment query parameter is provided).

If this field is false, then the number returned in num_identity_overrides is not an exact representation of the number of identity overrides, so the FE should concatenate the number with a + afterwards.

[tiagoapolo]

On hold until #4840 is merged.

[tiagoapolo]

Testing it

[tiagoapolo]

I tested using 1000+ identity overrides for a feature and I did not succeed to get is_num_identity_overrides_complete as False. Therefore I could not see the + sign being used.

cc: @zachaysan

[tiagoapolo]

Confirmed! Plus signed shows when is_num_identity_overrides_complete = False