Shutdown MetricsSystem when stopping MetricsService

[fab-10]

PR description

Shutdown MetricsSystem when stopping MetricsService, so any registered collector is cleaned, that is most useful during acceptance tests.

Fixed Issue(s)

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• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[lxcmyf]

besu/metrics/core/src/main/java/org/hyperledger/besu/metrics/prometheus
/MetricsPushGatewayService.java
I noticed that there is an implementation based on the Prometheus push data pattern here, and I would like to know if this push is long-term or temporary? Because Prometheus has explicitly stated that pushgateway is only suitable for short-term temporary data push usage.
@fab-10

[fab-10]

@lxcmyf since the introduction of the push gateway predates me, I searched why it was introduced and found the original requirement here 319ee20, so it should only be used if the normal pull mode is not feasible