Check admin endpoint instead of metrics for Pulsar WaitStrategy.

[nahguam]

Fixes #5513

[eddumelendez]

Besides the suggestion, my little concern is related to METRIC_ENDPOINT (which I am not expecting to be used) can break someone else code. I would rather deprecate it for now.

Would like to hear from @kiview @bsideup regarding to this.

In case, we agree to drop it. The following is needed in the build.gradle file in the pulsar module

tasks.japicmp {
    fieldExcludes = [
        "org.testcontainers.containers.PulsarContainer#METRICS_ENDPOINT"
    ]
}

[kiview]

I agree with @eddumelendez's argument and that's how we generally approach changes to the public API. So although unlikely that users depend on it, let's deprecate METRIC_ENDPOINT to be safe.

[eddumelendez]

@nahguam thanks for your contribution! this is now in master