Rename the builder group chromium.packager to chromium.infra

All existing builders in this group are technically infra related.
Rename the group so that it can fit other infra related builders

Bug: 1260195
Change-Id: I1199cb4c182b2e85331ca61a481cafc9cacdb04c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4459747
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/main@{#1134663}
NOKEYCHECK=True
GitOrigin-RevId: 9c454e5e6157ee8407487c7c19cc699f4ecfd2f9