[roll third_party/pigweed] pw_build: Generate setup.cfg files

Modify generated_python_package to create setup.cfg files instead of
setup.py files. This will make for easier parsing of package data by
other build tooling.

pw_python_package's generate_setup option has been updated to follow
setup.cfg structure. Relevant sections should be nested in the correct
scope. For example here is the old format:

generate_setup = {
  name = "a_nifty_package"
  version = "1.2a"
  install_requires = [ "a_pip_package" ]
}

New format:

generate_setup = {
  metadata = {
    name = "a_nifty_package"
    version = "1.2a"
  }
  options = {
    install_requires = [ "a_pip_package" ]
  }
}

This will generate a setup.cfg similar to the example here:
https://setuptools.readthedocs.io/en/latest/userguide/declarative_config.html

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/56960

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: d14a0eef6256f0f..afb861c1eca3fe2
Roller-URL: https://ci.chromium.org/b/8838433940317807969
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8838433940317807969
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: If2214d9d0a3fbfd6c4fa8ef9469613225d755af1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/57745
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 d14a0ee..afb861c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d14a0eef6256f0f5aeea390edfbf6f235fdfe39e
+Subproject commit afb861c1eca3fe2a1f1f4e3d35ff1086d748c44c