Introduce EventObserverBase and EventBasedLogUploader classes

EventObserverBase is the base class that implements the logic of
observing events and triggering event based log upload.
EventBasedLogUploader is the class that's responsible for collecting the
related logs to the event and upload them. Leave UploadEventBasedLogs()
function empty as placeholder becausew the actual upload logic is
blocked on server side changes. The classes that are added to this CL is
not yet called by anyone.
Add a new filepath chrome/browser/ash/policy/reporting/event_based_logs/
to contain all code related to event based log uploads. Add a new
dependency on chrome/browser/ash/policy/reporting/DEPS to be able to
call code from //chrome/browser/support_tool.

See go/cros-eventbasedlogcollection-dd for more details.

Bug: b:330675609
Change-Id: Ia1bf4c77a60342869fd63290b6546ff4e51da473
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5522606
Reviewed-by: Jeroen Dhollander <jeroendh@google.com>
Reviewed-by: Andrei Nedoluzhko <nedol@google.com>
Commit-Queue: Irem Uguz <iremuguz@google.com>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1300619}