Using slog for logging

[victornicolet]

We should use slog for logging instead of our custom config.LogGroup. However, we're using 5 different levels of logging (ERROR, WARN, INFO, DEBUG, TRACE) as opposed to four levels in slog (no TRACE level). It's useful for us to have TRACE and DEBUG separately since TRACE is specifically to trace information in dataflows. The amount of logging depends on the program being analyzed, whereas debug amount is relatively more stable.
We can use slog with an additional flag in the config to mark whether trace level should be logged as debug.

[github-actions]

Stale issue message