internal/postgres: treat new modules like large modules
internal/postgres: treat new modules like large modules

Don't enqueue more than largeModulesLimit new modules, in addition to
using that limit for large modules.

Some new modules are large, and sometimes the worker does get a big
batch of those new, large modules all at once. Its gets stuck
processing them and makes little to no progress.

Treating all new modules as large will result in processing pauses
when the modules are small, but at least we'll be able to see that
happening and gain some insight into the requeuing behavior.

Updates b/162495665.

Change-Id: I02319fbcec02d97b457638da31c8bf632d43955e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/245917
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite