lib/log: investigate logfmt or better-for-local-dev encoders

Created by: bobheadxi

Right now we just use Zap's default "human-readable" console format, which is not terribly readable because it dumps all attributes as JSON:

There are a few custom encoders out there we might be able to use, e.g. https://github.com/sykesm/zap-logfmt but I haven't experimented with them yet. I also wonder if there are better ones out there for Zap that's not strictly logfmt that we can use instead

See discussion: https://github.com/sourcegraph/sourcegraph/pull/35105#issuecomment-1121406416