[FEATURE] Default labeling rule for security based tenancy labeling

Is your feature request related to a problem?
As part of the effort to introduce multi-tenancy as a construct in OpenSearch (https://github.com/opensearch-project/OpenSearch/issues/13341), we are introducing a labeling service to attach tenancy labels to search requests. Plugins can define their rules to compute labels based on the given request and thread context. We need to add a "default" labeling rule in security plugin to get the tenancy information if the cluster is using security plugin as their auth method as part of https://github.com/opensearch-project/OpenSearch/pull/13374

What solution would you like?
Add a default labeling rule so that we can attach user info in a request.

What alternatives have you considered?
We can also maintain all rules in the core repo, but it would be better to let plugins implement their own rules, which would get registered with the RuleBasedLabelingService in core.

Do you have any additional context?
Please see
https://github.com/opensearch-project/OpenSearch/issues/13341
https://github.com/opensearch-project/OpenSearch/pull/13374

Start by reading OpenSearch issue 13341 and pull request 13374 to understand the labeling service contract and tenancy context. Then inspect how the security plugin can register a default labeling rule and determine how user information is obtained; done means the rule is registered and attaches the expected user tenancy information to requests.