--readonly mode allows to edit local files

[azat]

To Reproduce
Steps to reproduce the behavior:

• run rill locally in folder with --readonly (rill start --readonly)
• try to edit any file - it will be modified

Expected behavior
The file should not be modified

Additional context
Here #5039 (comment) @begelundmuller already wrote about the same issue I guess, but it will be nice to limit the editions even for local deployment