[FLINK-27050][runtime] Removes default RpcSystem instance

[XComp]

What is the purpose of the change

Having a default RpcSystem in TestingDispatcher.Builder
caused threads being spawned without cleanup. Instead, we
should rely on the RpcSystem instance provided by the test.

Brief change log

• Removed the default instance from TestingDispatcher.Builder and made it a required parameter through the build method

Verifying this change

• Running a test manually in a loop and checking that there are no threads left hanging, e.g. in DispatcherCleanupResourcesTest:

    @Test
    public void foo() throws Exception {
        for (int i = 0; i < 100; i++) {
            setup();
            testDuplicateJobSubmissionDoesNotDeleteJobMetaData();
            teardown();
        }

        System.out.println("Stop the debugger here");
    }

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 59722c6 Azure: FAILURE

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[zentol]

+1

[XComp]

I'm investigating the OOM in the integration tests of the flink-tests module (ci run). In the mean time, I'm gonna start another ci run

[XComp]

@flinkbot run azure

[XComp]

Force push without additional changes to trigger the CI since the run azure didn't seem to have worked...

[XComp]

Again force-pushed without any additional changes to trigger ci once more...

[zentol]

@flinkbot run azure

[XComp]

Rebased to most-recent master

[XComp]

Force-pushed once more after the branch idle'd for 5 days to prepare the merge for tomorrow morning...

[XComp]

Error caused by FLINK-26621 which is unrelated to this change.