[FEATURE] Track new engine test coverage

[MaxKsyunz]

Is your feature request related to a problem?
As a developer, I'd like to know when the v2 SQL engine has the same test coverage as the legacy engine.

We can begin planning deprecation of the legacy engine once this test coverage parity is reached.

What solution would you like?
A separate workflow that runs SQL plugin unit, integration, and doc tests with v2 engine only.

Test reports to be published as part of run results using an action such as

• https://github.com/test-summary/action
• https://github.com/marketplace/actions/test-reporter
• https://github.com/marketplace/actions/junit-report-action

[acarbonetto]

This would be helpful to track #787

[MaxKsyunz]

@acarbonetto @dai-chen

Let's have a "deprecate v1 engine" feature branch and update SQL Java CI workflow to track test coverage.

We need some way to run tests without V1 engine. The common way to implement this is via feature flags. However these would be run-time options (either JVM options or Spring feature toggles) and that's something we are trying to avoid.

It will be a bit of extra work to keep the branch up-to-date with most recent development branch, but I expect fast-forward merge will work most of the time and in the end, removing V1 engine will be trivial -- just merge the feature branch into dev.