`extendedUsage = clientAuth` is configured in server certificates

According to the docstring in `configure_client_authorization()` function [1], "clientAuth" extendedUsage should be added to the server certificates only if `tls.client.authorization.required` flag is set. However I can't find anything that would check for this condition and it seems that the "clientAuth" is added to the "extendedUsage" by default.

I'm not sure if the docstring is outdated or the conditional check is missing (or it's there and I somehow missed it).

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[1] https://github.com/charmed-kubernetes/layer-easyrsa/blob/44f635b92624be5882c70ca1544d79f5d8483e24/reactive/easyrsa.py#L134