Make multi-stage-query (MSQ engine) a core capability of Druid rather than an extension

[kfaraz]

Description

Druid MSQ engine offers a very convenient method of performing SQL-based batch ingestion, export, etc.

Given the importance and heavy adoption of MSQ, this patch converts MSQ into a core capability of Druid
rather than an extension, as was always intended.

Changes

• Move all MSQ classes to services module without renaming the package
• Move the module loader file org.apache.druid.guice.DruidModule to services/src/main/resources/META-INF/services
  • This effectively means that the modules listed in this file will always be loaded on all Druid services as desired
• Update dependencies as needed
• Remove mentions of extension from example common.runtime.properties files

Alternative

Instead of moving everything to services, the alternative was to simply move the
multi-stage-query module into a top-level module but that would
lead to cyclic dependencies between services and multi-stage-query since:
a) multi-stage-query depends on services for various classes
b) services is the entry point and must depend on all the core modules that need to be on the classpath

Pending

• Once initial feedback is received, the docs will also be updated to remove mentions of the multi-stage-query extension.

Future

• Over time, various MSQ classes may be moved out of services module into more appropriate modules such as
  processing, server, indexing-service or sql as applicable.

Release note

• Multi-stage-query (MSQ engine) is now a core capability of Druid rather than an extension.
• Remove druid-multi-stage-query from druid.extensions.loadList in common.runtime.properties.

Upgrade notes

While upgrading, the extension druid-multi-stage-query must be removed from druid.extensions.loadList.
Otherwise, Druid services would fail to start as they would not be able to locate this extension.

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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.

[kfaraz]

Closing in favor of #18394