adding description info to the fileDsc seciton in DDI CodeBook. #5051

[landreev]

What this PR does / why we need it:

Apparently, users have been asking for this since 2018 - for tabular files that have the Description field populated, this label was never exported in the DDI (non-ingested files always had their descriptions exported, in the corresponding <otherMat> sections).
There is no obvious field under <fileDscr> in the DDI Codebook schema for it - probably the reason we chose not to export it back in the day (?) - but putting it into another dedicated free text <note> field seems like a reasonable solution.

The RestAssured export tests are passing, so un-drafting the PR.

I kept the changes minimal to stay under the "3" estimate.

Which issue(s) this PR closes:

• Closes File description metadata of ingested files are not in the DDI exported metadata #5051

Special notes for your reviewer:

Suggestions on how to test this:

Straightforward. Upload some file that's known to be ingestable (Stata, CSV ... doesn't matter). Populate the description field in the file metadata. Publish the dataset. Look at the DDI export, the description should not be showing in the corresponding <fileDscr ...>, like this:

<notes level="file" type="DATAVERSE:FILEDESC" subject="DataFile Description">
   This is a tabular file produced from a Stata .dta file with rich descriptive metadata
</notes>

For extra credit, look at the file under Data Explorer, verify that new <notes> element isn't causing any trouble there (the Explorer relies on the DDI for viewing and - in the latest version - editing).
Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Is there a release notes update needed for this change?:

Additional documentation:

[coveralls]

coverage: 20.867% (-0.001%) from 20.868%
when pulling 84e0fad on 5051-ddi-tabular-file-description
into d039a10 on develop.

[github-actions]

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[pdurbin]

Overall, looks fine. I'm trusting that "notes" is the right place to put the file descriptions. I did leave a couple other comments.