Export particular channel groups

[FOSS-Love]

Checklist

• [x] I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• [x] I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• [x] This issue contains only one feature request. I will open one issue for every feature I want to request.

Describe the feature you want

I would like to create an export of subscribed accounts but not all of my subscribed accounts just the accounts that i kept under a group Music.

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

Additional context

How will you/everyone benefit from this feature?

I like to share best content providers with my friends, but not everyone is interested in all the content i follow, so to be able to send a group-subscription export file to a friend so that it would be easy to share.

[dev-victoria]

+1 I would therefore also like to import into a Group.

There's currently a few questions as discussion for me.

1. Should the used file(json) be compatible with the existing import/export of subscriptions? Pros: Allows mixing and matching Cons: User might accidentally pick the wrong one
2. If compatible should there be additional information in the file(to be understood by both new and existing functionality) This could and maybe should be used for warnings or a kind of "save as" dialog
3. Where do we place the export/import button We would need to add some kind of dialog for picking or change on the current channel group details layout.
4. Should we append this to #3590 as an Add-on It might be fitting to add the import/export functionality as a button to what is being created to solve that request.