Support Stackdriver ID and HTTPRequest

[nhooyr]

Support in error reporting too.

See

• https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry
• https://godoc.org/cloud.google.com/go/errorreporting#Entry

[nhooyr]

There's no good clean way to support this while remaining backend agnostic so closing.

[nhooyr]

the id in particular is superceded by the trace ID and HTTPRequest doesn't seem that important to me and would require some sort of middlewere which is def out of scope for slog.