xprofile Administration - Text field for Field group title may need to be labelled

[imath]

When we create a new group of profile fields, i think an information about what the text field for the group title expects may be interesting. I saw there was a label with a class set to screen-reader-text which if i understand correctly will show only on screen readers. In the diff attached, i suggest to add a placeholder.

[boonebgorges]

Something like this would be nice.

[boonebgorges]

In 7417:

Add placeholder text for xprofile field group title field.

This will help with accessibility and usability.

Fixes #5069

Props imath