SQL release for Elasticsearch 7.10

[penghuo]

Major breaking change

1. The runner is in RestIntegTestTask has been moved to RestTestBasePlugin. The new introduced RestTestBasePlugin will apply the testClusters defined in TestClustersPlugin to all the Task inherit RestIntegTestTask. Thus, we defined the testClusters
2. Remove integTest task from PluginBuildPlugin.

Description of changes

1. Define the testClusters which will be used as runner for all the test tasks.

testClusters.all {	
    testDistribution = 'oss'
    plugin ":plugin"
}

2.Originally, the docTest use testClusters.integTest to run doc test. We define the new testCluster.docTestCluster for docTest and inherent the RunTask.

testClusters {
    docTestCluster {
        plugin ':plugin'
        testDistribution = 'oss'
    }
}
tasks.register("runRestTestCluster", RunTask) {
    description = 'Runs elasticsearch ODFE SQL plugin'
    useCluster testClusters.docTestCluster;
}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dai-chen]

LGTM. Thanks for the changes!