[FLINK-11304][docs][table] Fix typo in time attributes doc

[JaryZhen]

What is the purpose of the change

This pull request fix typo in time attributes docs

Brief change log

Fix typo in time attributes doc that DefinedRowtimeAttribute should be DefinedRowtimeAttributes. also, implemented getRowtimeAttributeDescriptors method in doc.

Verifying this change

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

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, Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

[twalthr]

Thank you @JaryZhen. Merging...

[hequn8128]

@JaryZhen Thanks a lot for the fixing! Looks good.
Best, Hequn

[twalthr]

Sorry, @hequn8128. I saw your comment too late. I will fix this in a hotfix commit before porting it to the other branches. Thanks.

[JaryZhen]

Hi, @twalthr I'd like to know why this PR finished by Closed not Merged ?

[twalthr]

@JaryZhen there are two ways of merging PRs. Either via Github or via the Apache Gitbot. I used Gitbot with a the This closes #... string in the commit message:

f6da761

[JaryZhen]

@twalthr thanks for tell me that. In addition, I noted that only a single rowtime attribute is support at the moment was wrote in sourceSink , so ... I think it's necessary to let user know in this page.