[FLINK-14611][runtime] Move allVerticesInSameSlotSharingGroupByDefault setting from ExecutionConfig to StreamGraph

[zhuzhurk]

What is the purpose of the change

allVerticesInSameSlotSharingGroupByDefault is currently for internal use only.
It's better to not add it in ExecutionConfig which is for user configurations.
This PR is to move it from ExecutionConfig to StreamGraph.

Brief change log

• Moved allVerticesInSameSlotSharingGroupByDefault from ExecutionConfig to StreamGraph
• Adjusted its usages

Verifying this change

This change is already covered by existing tests, such as BatchExecutorTest and StreamingJobGraphGeneratorTest*.

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

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Last check on commit 8d20db4 (Wed Dec 04 15:03:09 UTC 2019)

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[zhuzhurk]

@zentol would you help to review this change?
Per the discussion here and here, it's better to move this config out from ExecutionConfig. And StreamGraph would be a better place for it.