Ingest: differentiate `date_released` and `date_submitted`

[joverlee521]

On Slack, @emmahodcroft pointed out that we are labeling the release date as date_submitted in the metadata TSV. These two dates usually aligned for SARS-CoV-2 sequences, but there is a noticeable difference in monkeypox sequences:

Once NCBI Virus adds submission date to their available fields, we can pull and include both dates in the metadata TSV.

[j23414]

Top right date seems to be UpdateDate_dt

• https://github.com/nextstrain/ncov-ingest/blob/master/docs/ncbi-virus-all-fields-example.json#L235

Also described by NCBI documentation as "Modification date"

• https://www.ncbi.nlm.nih.gov/Sitemap/samplerecord.html