Consistent use of `domain`, `pages_domain` and `pages_host` in logs

Summary

In https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/15656#note_997409890 we are investigating how pages deals with traffic spikes and one thing that came up was how logs can be a bit confusing because not all log messages have pages_domain for filtering.

Ideally, we would probably have domain or pages_domain set for all log files. Right now, requests only use pages_host which is provided by the client, which means log entries are often split between example.com and example.com:443.