Add endpoint to upload file

[philipeleandro]

No description provided.

[danielnottingham]

I liked your solution! Maybe you could consider adding some test cases:
'imports a valid CSV file'
'handles an empty CSV file'
'returns an error for non-CSV files'

here I'm not sure if it's worth adding a test for this:

def encode_string(string)
  string.force_encoding("ISO-8859-1").encode("UTF-8")
end

'handle CSV files that contain special characters'

[philipeleandro]

@danielnottingham thanks! I created the PR and I forgot to add tests. Soon I'll add the tests