Enable field name translations to use "Custom translations"

Discussed in <div type='discussions-op-text'> ^{Originally posted by ruihildt July 24, 2023} Summary Custom translations are useful because you can centralize all translations in the same place. Basic Example _No response_ Motivation Unfortunately, field name translations can't use the Custom translations. So sometimes you will have to duplicate translations, and not every translations will be centralized in the same place. Detailed Design Next to the "Create new" button (or instead), add the translation icon to make it possible to select an existing custom translation Requirements List Must Have: • easy pick from the Custom translations Drawbacks No drawbacks. :) Alternatives Don't do anything and keep the issue unsolved. Adoption Strategy If you already have translation, I guess it would be nice to offer to add them to the Custom translations. Ideally this coul…