Enhance Javadoc documentation for WordCount Tokenizer class

[Diogo-Sardagna]

Updates the Javadoc for the WordCount.Tokenizer class to provide a clear and structured explanation of its behavior. The new documentation outlines the purpose of the class, how the input is normalized, how tokens are generated, and under what conditions they are emitted. It also includes structured HTML formatting for improved readability. This enhancement facilitates understanding for new contributors and readers of the codebase, aligning with the documentation quality expected in Apache Flink examples.

[flinkbot]

CI report:

• 98623949891f6f080d5df5b51fa1609b2ef05fab Azure: FAILURE

Bot commands

The @flinkbot bot supports the following commands:

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

[davidradl]

@Diogo-Sardagna please associate this change the title to include a Jira or include hotfix as per the process