[NFC] Add metadata about import jobs to MapField form

[NFC] Add metadata about import jobs to MapField form

This extra metadata has been part of a whole lot of PRs & somehow always
winds up in conflict or otherwise so I'm adding it by itself, wihout any usage of it.

Note that
- this brings MapField into line with DataSource
- there is nothing calling these functions as of this PR - it's just
an attempt to get the extra metadata added to the forms/ parsers without
conflict