Timestamp issue with Open Search

[jbrown-xentity]

The Open Search automatically assigned the DCAT-US modified field (https://resources.data.gov/resources/dcat-us/#modified) to be some type of date field. This is causing problems, as not all values are of the same schema. We currently accept quite a few formats (regex here). We should probably change this field to just be a string type. It will limit ability to sort on that field, but not sure we support that today anyways.

How to reproduce

1. Review recent job of openSearch indexing. Note any errors (many)
2. Review missing examples of values with something like R/P1M.

Expected behavior

No (or minimal) index errors)

Actual behavior

Index errors

Sketch

We should change the field type for the modified field in the dcat object to be just a string, that's how it comes in. More research is needed to understand how that should be accomplished.
See slack thread for more background.