[roll third_party/pigweed] pw_software_update: Add user_manifest bundle arg

This change adds a user-defined "user_manifest" option to the GN
template for creating update bundles. The user manifest is treated like
any other target payload for the purpose of bundle creation, but has a
unique API on the GN side because it will be treated differently in the
update client on the firmware side.

Tested: Built downtream with and without user_manifest
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/65360

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 12ea8d02bc538d1..6fe3045f7d8c581
Roller-URL: https://ci.chromium.org/b/8833449280228392065
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8833449280228392065
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie6d491e559c0223225814d2e02e4f94d0322d9a1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/65521
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 12ea8d0..6fe3045 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 12ea8d02bc538d1e94b3f0788192f33380ccac55
+Subproject commit 6fe3045f7d8c5810999f493bd1d239c34d60d69c