This function reads a KOSIS API key from a specified file and
sets it for use in KOSIS API calls.
Arguments
- file
A character string specifying the path to the file
containing the KOSIS API key.
Value
No return value. A message will be printed to confirm
that the key has been set.
Details
The file should contain the API key as a single line of text.
If the file does not exist, an error will be raised.