[Improve][Doc][connector-file] Document SaveMode options for HdfsFile/LocalFile

[yzeng1618]

Purpose of this pull request

• Align HdfsFile sink with other file sinks (e.g. SftpFile/FtpFile/S3File/LocalFile) by exposing and documenting schema_save_mode and data_save_mode.
• Add schema_save_mode / data_save_mode into HdfsFileSinkFactory OptionRule so configs using SaveMode are not rejected by option validation.

Does this PR introduce any user-facing change?

Yes.

• Users can now configure schema_save_mode and data_save_mode for HdfsFile sink without failing option validation.
• Documentation is updated accordingly.
• Runtime semantics are unchanged (SaveMode behavior already exists); this PR mainly makes the options discoverable/usable and keeps docs consistent.

How was this patch tested?

No

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• [ * ] If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If necessary, please update incompatible-changes.md to describe the incompatibility caused by this PR.
• If you are contributing the connector code, please check that the following files are updated:
  1. Update plugin-mapping.properties and add new connector information in it
  2. Update the pom file of seatunnel-dist
  3. Add ci label in label-scope-conf
  4. Add e2e testcase in seatunnel-e2e
  5. Update connector plugin_config

[davidzollo]

+1
Good job

[corgy-w]

LGTM

[davidzollo]

+1