Add a metric for task duration in the pending queue

[rockc2020]

Description

This PR is to measure how long a task stays in the pending queue and emits the value with the metric task/pending/time. The metric is measured in RemoteTaskRunner and HttpRemoteTaskRunner.

An example of the metric:

2022-04-26T21:59:09,488 INFO [rtr-pending-tasks-runner-0] org.apache.druid.java.util.emitter.core.LoggingEmitter - {"feed":"metrics","timestamp":"2022-04-26T21:59:09.487Z","service":"druid/coordinator","host":"localhost:8081","version":"2022.02.0-iap-SNAPSHOT","metric":"task/pending/time","value":8,"dataSource":"wikipedia","taskId":"index_parallel_wikipedia_gecpcglg_2022-04-26T21:59:09.432Z","taskType":"index_parallel"}

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Key changed/added classes in this PR

• Emit metric task/pending/time in classes RemoteTaskRunner and HttpRemoteTaskRunner.
• Update related factory classes and tests.

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This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[clintropolis]

seems reasonable to me 👍