Add query templates to catalog

[jon-wei]

This PR adds a feature to the Druid catalog for storing query templates that can be referenced when issuing queries via Druid SQL.

An initial "concat" template is implemented, which stores a portion of a query that will be appended to a variable query portion submitted at query time.

This PR has:

• [x] been self-reviewed.
• [ ] 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.
• [x] been tested in a test Druid cluster.