Add option to exclude metadata in downloading features

[rjonesey]

I'm running into an interesting issue in parsing the JSON of the photo's metadata. There are a lot of weird character strings that are causing the parsing function to fail. In my current use case, I don't have a need for the images metadata. If possible, I'd like to exclude the metadata from the query_layer_attachments function altogether. I also wonder if an option here would be to build an identical function that utlizes the jsonlite package instead of Rccpsimdjson? Just for that one fparse function we could instead use the parser from jsonlite, which I think for some reason can handle the weird character strings, but is a bit slower. Thoughts?