cros: metrics: shill: Add metrics for DHCPv4 provision result

Adds two metrics, DHCPv4RenewRebind and DHCPv4ProvisionResult, that
track ChromeOS network performance related to DHCPv4 provision. See
https://crrev.com/c/6481673 and https://crrev.com/c/6486130 for the
details of metric emission.

Bug: 397523142
Test: None
Change-Id: Ib3d27b30c62cb50b73d3ac00ce5796f19547ba38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6579167
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Commit-Queue: Zikai Chen <chenzikai@google.com>
Cr-Commit-Position: refs/heads/main@{#1465352}