configure batch size to send audit/logger events
in batches instead of sending one event per connection.
this is mainly to optimize the number of requests
we make to webhook endpoint.
When setting a config of a particular sub-system, validate the existing
config and notification targets of only that sub-system, so that
existing errors related to one sub-system (e.g. notification target
offline) do not result in errors for other sub-systems.
Also log all the missed events and logs instead of silently
swallowing the events.
Bonus: Extend the logger webhook to support mTLS
similar to audit webhook target.
This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`
