Rename NetworkHealthService to NetworkHealthManager

Currently NetworkHealth implements mojom::NetworkHealthService
and NetworkHelathService wraps the ash implementations of
mojom::NetworkHealthService and mojom::NetworkDiagnosticsRoutines.

This is part 1/4:
1. chrome/browser/ash/net/network_health/NetworkHealthService
   -> NetworkHealthAsh
2. chrome/browser/ash/net/network_health/NetworkHealth
   -> chromeos/services/network_health/NetworkHealthService
3. chromeos/services/network_health/in_process_instance.cc owns
   the browser global NetworkHealthService instance, available to
   Ash code outside of src/chrome.
4. chromeos/services/network_health/public/cpp/network_health_helper
   provides a helper class for observing either an in-process instance
   (on Ash) or a remote instance (on Lacros) and tracking the active
   networks.

The NetworkHealthHelper class will be used by
content/browser/renderer_host for providing suggestions based on the
default network state (i.e. captive portal state) on Ash or Lacros.

BUG=b:250725789
TEST=Code compiles, unit tests

Change-Id: I8467ce01933784dab8af4cd4180f6333498d78bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3933896
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Auto-Submit: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Kartik Hegde <khegde@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1056524}