basic auth: add option to exclude bcrypt at build time

[jan--f]

This add the option to exclude bcrypt during the build process by passing -tags nobcrypt. Currently this disables user authentication via basic_auth. If authorized users are configured but the server is build with nobcrypt the endpoint will respond with Unauthorized, even if the correct credentials are send. The goal is to be able to exclude bcrypt for compliance reasons. In the future we could add basic_auth using other hash functions.