If a user wants to create an index on the field "aField" and it's not found in the sampled field names, however, when another field with a name that contains that field, like "aFieldWeDontWantToIndex", exists we can't enter that into the `CreateIndexFields` combobox:

We should allow entering a substring of a field as a field. Let's give an additional option when typing, shown as the last option, that is the text that is typed (when there is typed text).