Fix druid client timeout zero

[clintropolis]

Description

The documentation specifies that using a timeout of 0, however this was actually a lie and specifying a timeout of 0 would cause a query to timeout and fail immediately.

This PR fixes this issue, but also doesn't completely allow infinite timeout to be totally within the users control (with no way for the server-side to mitigate) so instead allows 0 to use the maximum server-side timeout druid.server.http.maxQueryTimeout, which defaults to Long.MAX_VALUE so is effectively unlimited unless explicitly configured by operators.

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This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• 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.
• been tested in a test Druid cluster.