Support multiple values for a key param

[lionick]

We need to change the implementation of to_urlencoded to support the doseq option of the urllib.parse.urlencode function.

The documentation is here: https://docs.python.org/3/library/urllib.parse.html#urllib.parse.urlencode

[c00kiemon5ter]

This is needed to construct URLs with multiple values of a query param.

Specifically, the Resource Indicators RFC allows specifying multiple target resources to be included as part of the aud claim for a generated token.

[rohe]

@lionick can you rebase this (and the other PRs you have) onto the present main ?

[lionick]

@rohe I have rebased it. When merged, I will rebase and the other.