Make unsaved changes in the annotation guide editor more resilient

[zhiltsov-max]

Actions before raising this issue

• I searched the existing issues and did not find anything similar.
• I read/searched the docs

Is your feature request related to a problem? Please describe.

If I leave the editor page with unsaved changes in the annotation guide editor, there's nothing to prevent it. The data is also is not saved neither in the browser, nor on the server. Annotation guides can contain a lot of text, and occasionally losing the editing progress is undesirable.

Extracted from #6536

Describe the solution you'd like

No response

Describe alternatives you've considered

• Use local storage to save the copy of the guide while editing (preferred)
• Show a notification about unsaved changes on leaving the page

Additional context

No response

[prathamesh-patil-5090]

Hey @zhiltsov-max checkout - #10340