[ZEPPELIN-3438] Passing Z variables to BigQuery interpreter

[sanjaydasgupta]

What is this PR for?

This PR enables the interpolation of ZeppelinContext objects into the paragraph text of BigQuery cells. It also introduces a new interpreter-level configuration parameter named zeppelin.bigquery.interpolation. This new parameter is false by default, and must be set to true to enable object interpolation. The default value of false guarantees backward compatibility for users who are not aware of the new feature.

The implementation takes the same approach that was followed in PR 2898 and 2903.

What type of PR is it?

[Feature]

Todos

• - Task

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-3438

How should this be tested?

Two new unit test classes have been added: BigQueryInterpolationDefaultTest.java, and BigQueryInterpolationEnabledTest.java.

Also, the code in this PR merely causes the BigQuery interpreter to "opt-in" to the implementation already existing in the Interpreter base class - described in PR-2898. The unit tests necessary are already present in PR-2898

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? Yes, documentation changes provided in bigquery.md

[sanjaydasgupta]

Need to make corrections in my repo, so am closing this PR now. Will be back with a new PR later.