Remove logging library references

[livio-a]

Currently this library uses our logging library. Since zitadel/zitadel#11159, the library is deprecated. We should use the global slog loggers instead. Zitadel already populates context data in middleware, so this does not have to be handled by SAML anymore.

Acceptance criteria

• Use the slog global logging functions
• Remove all references to https://github.com/zitadel/logging
• Update documentation / readme and explain the global / default logger is now used and how to disable that if not wished.