Change HildCog required field error to Name

[CarolineDenis]

Fixes #6099

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone

Testing instructions

• Go to a COG that has a child COG or create one.
• Expand the child COG and remove the name of the child COG.
• Collapse subview
• Attempt to save.
• verify that the warning message is: Name: Field is required

[combs-a]

• verify that the warning message is: Name: Field is required

It's now using field's chosen name which is much better 👍

It could potentially specify it's an error in the childCOG, but I think this edge case (where Specify cannot highlight the actual field due to a form issue, and instead has to use a dialog) is unlikely to be encountered very often (hopefully).