Fix error messages in Characteristics Batch upload endpoint

Beckers, Harper N
2022-03-08T17:31:11Z

*Created by: amedenblik*

There is an error with the POST Characteristics Batch Upload endpoint: https://streamstats.usgs.gov/docs/gagestatsservices/#/Characteristics/POST/CharacteristicBatchUpload

Example: you attempt to upload 10 characteristics. The first 5 are uploaded successfully. The next characteristics are not uploaded successfully because they are missing the "stationID" element. The X-USGSWIM-Messages still says `"{"info":["added 10 items."],"error":["An error occurred while updating the entries. See the inner exception for details."]}` even though only 5 items were added. The info/error messages need to be improved so they are more accurate/helpful.