This is a helper to determinine which extension should be used for a file. Two types of input are acceptable:
MIME types accepted by Google Drive.
File extensions, such as "pdf", "csv", etc. (these are simply passed through).
Examples
## get the extension for mime type image/jpeg
drive_extension("image/jpeg")
#> [1] "jpeg"
## it's vectorized
drive_extension(c("text/plain", "pdf", "image/gif"))
#> [1] "txt" "pdf" "gif"