This function takes a map of lists of strings and inverts it so that
the string values become keys and the keys become items within the
corresponding lists.
This escapes all characters that might have a special interpretation when embedded into a portion of a URL, including slashes, equals signs and ampersands.
Since Terraform's internals are not 8-bit clean (it assumes UTF-8
strings), we can't implement raw gzip directly. We're going to add
support where it makes sense for passing data to attributes as
base64 so that the result of this function can be used.
Ariel Alonso