Add tracing support to ES Security

[ankit--sethi]

Adding tracing support for the authenticate action by wrapping theauthenticator.authenticate call in AuthenticatorChain with startTrace/stopTrace actions.

In synchronous contexts, spans are stored in ThreadLocal objects under the hood and the currently active span look up (needed to end a span, append metadata, or spawn a child span) can be implicit. However, to track a span across threads as ActionListener pattern requires, we need to make Authenticator.Context implement Traceable which defines a random, unique spanId for each Authenticator.Context object, enabling us to uniquely locate the associated span regardless of which thread is currently executing.

Sample trace when running locally with ./gradlew :run --with-apm-server:

{
    "transaction":
    {
        "timestamp": 1755816123929000,
        "name": "authenticate", <------- supplied span name
        "id": "4a6498d97c2349d2",
        "trace_id": "c44f5269a1ff1e215bdd151d41df8b2d",
        "type": "unknown",
        "duration": 25.189,
        "outcome": "unknown",
        "context":
        {
            "service":
            {
                "framework":
                {
                    "name": "OpenTelemetry"
                },
                "version": null
            },
            "tags":
            {}
        },
        "span_count":
        {
            "dropped": 0,
            "started": 0
        },
        "dropped_spans_stats":
        [],
        "otel":
        {
            "span_kind": "INTERNAL",
            "attributes":
            {
                "es.cluster.name": "runCluster",
                "es.node.name": "runCluster-0",
                "security.authenticator.type": "cloud API key" <---- supplied custom field
            }
        },
        "sample_rate": 1.0,
        "sampled": true
    }
}

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)