internal/config: the override bucket matches the project ID
internal/config: the override bucket matches the project ID

Instead of a fixed override bucket, use the bucket named after the project ID.

Change-Id: I40743350db9359dd23368b98a2832e5eeadb3ce9
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/254097
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

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