[wpt] Upload a compact version of each wptreport

Currently, running all WPTs on WebView generates ~220 MB of wptreport
data. With more platforms, updating metadata will be untenably slow and
place pressure on the ResultDB infrastructure.

In this change, the WPT results processor uploads a "compact" version
of each report when wptrunner did not use the upstream repo. Using the
upstream repo indicates the report is intended for upload to wpt.fyi,
which requires all fields. Both versions are uploaded with extraneous
JSON whitespace removed.

For compact reports, the amount downloaded per builder decreases to
~140 MB.

Bug: 1299650
Change-Id: I7eac366449af352b2abbbe4a6288fac1809bdbc7
Cq-Include-Trybots: luci.chromium.try:linux-wpt-identity-fyi-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3864504
Commit-Queue: Jonathan Lee <jonathanjlee@google.com>
Reviewed-by: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1041560}