[DOC] Update documentation for obfuscate processor

[Utkarsh-Aga]

What do you want to do?
Starting Data Prepper 2.8, single_word_only option was added to the obfuscate processor, but the documentation does not talks about it, thus adding the same to the documentation.

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request and all versions that are affected.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
Pull request for single_word_only option.

[hdhalter]

This is closed by #7251.