providers/proxy: fix URL path getting lost when partial URL is given to rd= (#11354)
* providers/proxy: fix URL path getting lost when partial URL is given to rd=
* better fallback + tests
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Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Co-authored-by: Jens L. <jens@goauthentik.io>