For all OSS plugins (except repository-* and discovery-*) integTest
task is now a no-op and all of the tests are now executed via a test,
yamlRestTest, javaRestTest, or internalClusterTest.
This commit does NOT convert the discovery-* and repository-* since they
are bit more complex then the rest of tests and this PR is large enough.
Those plugins will be addressed in a future PR(s).
This commit also fixes a minor issue that did not copy the rest api
for projects that only had YAML TEST tests.
related: #56841
This merges the code for the `significant_terms` agg into the package
for the code for the `terms` agg. They are *super* entangled already,
this mostly just admits that to ourselves.
Precondition for the terms work in #56487
This moves the testing of custom significance heuristic plugins from an
`ESIntegTestCase` to an example plugin. This is *much* more "real" and
can be used as an example for anyone that needs to actually build such a
plugin. The old test had testing concerns and the example all jumbled
together.