providers/oauth2: remember session_id from initial token (#7976)
* providers/oauth2: remember session_id original token was created with for future access/refresh tokens
* providers/proxy: use hashed session as `sid`
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Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Co-authored-by: Jens L <jens@goauthentik.io>