[FLINK-27265][docs] Flink comes with five built-in BulkWriter factories instead of the mentioned four in filesystem.md.

[empcl]

What is the purpose of the change

in filesystem.md, flink comes with four built-in BulkWriter factories, in fact, the list has five.

Brief change log

in filesystem.md, flink comes with four built-in BulkWriter factories, in fact, the list has five.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

yes

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

[flinkbot]

CI report:

• ab93146 Azure: SUCCESS

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[MartijnVisser]

@chenlei677 Thanks for the PR. Please check and follow the code contribution guide at https://flink.apache.org/contributing/contribute-code.html and update your PR, else it can't get merged.

[MartijnVisser]

@empcl Thank you for the PR. For your next PR, please make sure that you're following Flink's Code Contribution Guide as documented at https://flink.apache.org/contributing/contribute-code.html

I've fixed your commit message this time and corrected the PR, but this is normally not done by someone in the community but should be taken care of by the contributor.