Code Coverage additions for Extensions

[ashwintumma23]

Description

• Contributes to code coverage for a few class in the extensions-core and extensions-contrib directories

Release note

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Key changed/added classes in this PR

• Prometheus Emitter
  • extensions-contrib/prometheus-emitter/src/test/java/org/apache/druid/emitter/prometheus/PrometheusEmitterConfigTest.java
  • extensions-contrib/prometheus-emitter/src/test/java/org/apache/druid/emitter/prometheus/PrometheusEmitterTest.java
• Multi-Stage Query
  • New: extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/indexing/MSQTaskListTest.java
  • extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/indexing/MSQTuningConfigTest.java
• Simple Client SSLContext
  • New: extensions-core/simple-client-sslcontext/pom.xml
  • New: extensions-core/simple-client-sslcontext/src/test/java/org/apache/druid/https/SSLClientConfigTest.java
  • New: extensions-core/simple-client-sslcontext/src/test/java/org/apache/druid/https/SSLContextProviderTest.java

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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.
• a release note entry in the PR description.
• 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.