refactor(wopi): postFile override handling into helpers and streamline logic

[joshtrichards]

• Target version: main

Summary

Refactor WopiController::postFile() to make WOPI override handling easier to follow by separating the main branches into focused helper methods for:

• RenameFile
• PutRelativeFile
• write-context validation

This turns postFile() into a clearer orchestrator and reduces the amount of mixed logic in the main controller method.

Notes

• Preserves existing behavior for WOPI lock operations
• Keeps RenameFile and PutRelativeFile paths isolated
• Improves readability and maintainability of the shared controller flow
• Returns HTTP_BAD_REQUEST for unsupported WOPI override values
• Fixes the RenameFile response shape so it no longer matches PutRelativeFile

The newly introduced resolveWopiWriteContext() helper can be used for future refactoring the various other WOPI operations handling paths in this class, eliminating a lot of boilerplate/duplication.

TODO

• Make sure nothing breaks (in theory this should be a non-eventful change externally...)
• Double-check tests
• Possibly add additional tests/coverage

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Documentation (manuals or wiki) has been updated or is not required