Add export capabilities to MSQ with SQL syntax

[adarshsanjeev]

Problem

Druid currently does not allow export of tables in a programmatic manner. While is is possible to download results from a SELECT query, this relies on writing the results to a single query report, which cannot support large datasets. An export syntax which writes the results in a desired format directly to an external location (such as s3 or hdfs) would be useful.

(INSERT/REPLACE) INTO
EXTERN(<external source function>)
AS <format>
[OVERWRITE ALL]
<select query>

For example: A statement to export all rows from a table into S3 as CSV files would look like

REPLACE INTO 
EXTERN(s3(bucket='bucket1', prefix='export/', tempDir='/var/temp'))
AS CSV
OVERWRITE ALL
SELECT * FROM wikipedia

Initially, only CSV is supported as an export format, but this can be expanded to support other formats easily.

Release note

• Adds export statements to MSQ, as a part of INSERT and REPLACE statements. This will allow the results of a query to be written to destination in a configurable format.

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Key changed/added classes in this PR

• sql/src/main/codegen/includes/common.ftl
• sql/src/main/codegen/includes/replace.ftl
• IngestHandler

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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.