Multi-logtype support

[michelemin]

Breaking config change

The config now needs to look like this

[loading.log_type_overrides]
"test_cron.wasm" = ["test_cron"]
"test_multi_logtype.wasm" = ["multilogtype1", "multilogtype2"]
...

I.e., on the right of the = sign, we now have an array and not a single string.