logging: relocate auto-generated log programs

[taroface]

The programs that generate the logging docs are located at pkg/util/log and pkg/util/log/eventpb/. They might be better located at pkg/cmd/docgen.

Jira issue: CRDB-3070

[blathers-crl]

Hi @taroface, please add a C-ategory label to your issue. Check out the label system docs.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is otan.}