Look for config in /usr as well

[DaanDeMeyer]

The UAPI group is trying to work towards working image-based Linux systems that contain only /usr (see uapi-group/specifications#76). To make this work it'd be great if rpm-sequoia would look for its policy in /usr/share/crypto-policies if the environment variables aren't set and no config file is found in /etc/crypto-policies

[nwalfield]

Sorry for not responding. In #72, I've changed rpm-sequoia to first look for the crypto policy in /etc/crypto-policies/back-ends/rpm-sequoia.config, and if that does not exist, /usr/share/crypto-policies/back-ends/rpm-sequoia.config.