[FLINK-36745][docs] Make FixedSizeSplitFetcherManager and FixedFetcherSizeSourceReader examples match Flink 2.0-preview API

[kaygorodov]

What is the purpose of the change

Examples on documentation page Data Sources have been using the APIs that do not exist anymore in Flink 2.0-preview.

• FixedSizeSplitFetcherManager uses a SplitFetcherManager constructor that accepts elements queue and was removed in Flink 2.0-preview https://issues.apache.org/jira/browse/FLINK-36245
• FixedFetcherSizeSourceReader uses uses a SourceReaderBase constructor that accepts elements queue and was removed in Flink 2.0-preview https://issues.apache.org/jira/browse/FLINK-36245
• FixedFetcherSizeSourceReader uses getInteger method of Configuration that was removed in in Flink 2.0-preview https://issues.apache.org/jira/browse/FLINK-34082

Brief change log

• switch FixedSizeSplitFetcherManager, FixedFetcherSizeSourceReader to use proper constructors of their super classes
• switch from getInteger to get method of the Configuration class

Verifying this change

• Since the changes affect the doc examples and there are no tests. I copied the snippets and verified (compiled) them locally.

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:

• 062cc2c Azure: SUCCESS

Bot commands

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

[lvyanquan]

LGTM.

[davidradl]

Reviewed by Chi on 21/11/24 Need a committer to review

[davidradl]

Reviewed by Chi on 21/11/24 Need a committer to review