Add `OsUpdateEventObserver` for event based log upload

`OsUpdateEventObserver` will observe `reporting::OsUpdatesReporter` and
upload logs when an OS update failure is detected. Add observer class
to `OsUpdatesReporter`. `OsUpdatesReporter` will create an upload ID
and notify the observers if the detected event is failure. Add new
`upload_id` field to `OsEventsRecord` proto to connect the log upload
and the reporting event on the server side. Add a getter to
`DeviceCloudPolicyManagerAsh` to attach the observer.
Separate `EventBasedLogUpload` into the virtual interface and Impl
class for testing purposes. Use a `MockEventBasedLogUpload` when
testing `OsUpdateEventObserver`. `EventBasedLogManager` will initialize
and own `OsUpdateEventObserver` instance. Convert
`EventBasedLogManagerTest` into a browser test because
`OsUpdateEventObserver` needs browser environment to be created.

Bug: b/330675033
Change-Id: I52a039af65481dc573500ea954ac9d2c896de9fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5633418
Commit-Queue: Irem Uguz <iremuguz@google.com>
Reviewed-by: Simon Hangl <simonha@google.com>
Reviewed-by: Alberto Juarez <albertojuarez@google.com>
Reviewed-by: Igor <igorcov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1316484}