(1.11) [FLINK-21132][runtime] Don't end input on stop with savepoint

[rkhachatryan]

What is the purpose of the change

(1.11 backport)

EndOfInput was used to handle any stopping of the job. When
stopping with savepoint the input is not actually ended.
This causes issues with some sinks (e.g. Iceberg).

With this change, endInput is not call for stop-with-savepoint.

To differentiate stop-with-savepoint from other cases
only checkpoint (RPC/barriers) are considered and not network EOP.
That's enough because EOP is only injected after the CP completion
(i.e. when the downstream is also notified by sync savepoint by CP
barriers).

Verifying this change

• Added SavepointITCase (testStopSavepointWithBoundedInput, testStopSavepointWithBoundedInputConcurrently)
• Added StreamTaskTest (testSyncSavepointAborted,testSyncSavepointAbortedAsync,testSyncSavepointCompleted)

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): yes (endInput is not called anymore for stop-with-savepoint)
• 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/Mesos, 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? no

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[pnowojski]

Thanks for the fix @rkhachatryan . As we discussed in the Jira ticket, I guess this is the best approach for the time being. I've left a couple of smaller comments.

One meta comment. First we added two test cases in SavepointITCase next to test network tasks better, we added a couple of more in StreamTaskTest. How much are those tests overlapping? Maybe we should have all end of input tests on the test harness level?

[rkhachatryan]

Thanks for reviewing @pnowojski !

The test failure was unrelated (FLINK-21216), rebased.
While debugging, I found a missing synchronization in StreamSourceTask (see below).

PTAL.

[pnowojski]

Thanks for the changes! Can you squash the fixup commits?