[Feature Request]: Syncing subscriptions with Invidious

### Guidelines

- [X] I have searched the issue tracker for [open](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aopen+is%3Aissue) and [closed](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+is%3Aclosed) issues that are similar to the feature request I want to file, without success.
- [X] I have searched the [documentation](https://docs.freetubeapp.io/) for information that matches the description of the feature request I want to file, without success.
- [X] This issue contains only one feature request.

### Problem Description

It'd be cool if we were able to sync our subscriptions with an invidious instance (this could also help keep freetube instances in sync)

### Proposed Solution

Allow user's to provide an authentication instance and an auth token (i think we should use the token for now instead of username and password as we'd need to find a way to securely store the username and password).

Invidious has api endpoints for: getting subscriptions, adding a subscription and removing a subscription.
https://docs.invidious.io/api/authenticated-endpoints/#get-apiv1authsubscriptions

### Alternatives Considered

Don't implement subscription syncing via invidious, it could be hard on their servers as there are no bulk endpoints that we can use for adding and removing subscriptions. We may also have some issues with removing subscriptions that we'd need to figure out ex: if someone removes a subscription on invidious, we'd likely end up readding that subscription with freetube, especially if there's multiple freetube instances

### Issue Labels

ease of use improvement, new feature, new optional setting, support for external software

### Additional Information

_No response_