feat: import export form

[cin-bun]

Checklist:

https://st.yandex-team.ru/DEVSHAD-271
https://st.yandex-team.ru/DEVSHAD-270

• The ticket number is indicated in the comments
• Unrelated code has been removed (unused imports, print statements, unrelated template context variables, commented code, etc)
• I translated the new messages and added only the .po files that actually changed.
• If there were changes in the frontend, there is a PR in the front repository.

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• I have added tests that prove my code works
• No common performance issues (e.g. N + 1 problem)

[cin-bun]

Тут еще ждем апрув от аскольда на выгрузку, но если и будут правки то косметические, основную логику и структуру можно смотреть