Remove logging library references

[muhlemmer]

Currently the OIDC server uses it own slog logger instance, based on our logging library. After zitadel/zitadel#11159, the library will be deprecated. OIDC should use the global slog loggers instead. Zitadel already populates context data in middleware, so this does not have to be handled by OIDC 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.