refactor: migrate from zap logger to log/slog

[knqyf263]

Description

Currently, we are using the zap library for logging in Trivy. However, to align with more standards, we have decided to migrate to the built-in log/slog package.

Since slog.Handler is an interface, projects that import and use Trivy can still utilize custom loggers. Although zap has better performance, it is not expected to be an issue for Trivy, as it does not output a large volume of logs.