use log/slog for structured logging

[seankhliao]

Overview

Switches pkg/log and logrus for the standard library's slog logger.

What this PR does / why we need it

This is more or less a mechanical replacement of the internal log.Logger interface and logrus logger with the standard library's slog. This appears to be the general community consensus on a standard logging interface, where slog.Logger is used as the common interface, and implementations can switch out the slog.Handler if necessary.

Connectors have their type and id added as attributes. Log lines are lowercased for consistency.

Closes #2020

Special notes for your reviewer

If dex is used as a library, this will be a breaking change. Log line output will be different from before.