Issue #597: Rename host response time to metricshub.host.response_time

[NassimBtk]

This pull request includes several changes to the ProtocolHealthCheckStrategy class and related test cases, as well as a modification to the metric names in the metricshub-host-metrics.yaml file. The most important changes include renaming metrics, updating the ProtocolHealthCheckStrategy class, and enhancing test coverage.

Metric Renaming:

• metricshub.host.up.response_time was renamed to metricshub.host.response_time in the metricshub-host-metrics.yaml file.

Updates to ProtocolHealthCheckStrategy:

• Changed the visibility of constants UP and DOWN from public to package-private and introduced new constants UP_METRIC_FORMAT and RESPONSE_TIME_METRIC_FORMAT for metric formatting in ProtocolHealthCheckStrategy.java.
• Refactored the run method to use the new metric format constants for collecting metrics.

Enhancements to Test Coverage:

• Added new import statements for assertEquals, assertNotNull, and Optional in ProtocolHealthCheckStrategyTest.java.
• Included NumberMetric import and updated the createTelemetryManagerWithTestConfig method to set strategyTime. [1] [2]
• Enhanced the testCheckHealth method to validate the metric values and ensure the metrics are not null. [1] [2]

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