[Feature Request]: Block channel by URL

### 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

Currently, channels can be blocked by their ID. This can be inconvenient, as many people may be holding the channel link, but will have to search for the Get ID option in YouTube / Invidious / etc. or manually delete most of the URL to paste it in.

### Proposed Solution

Enable blocking channels by URL:
1. For channel links of the form `*/:id`
2. For channel links without channel ID (e.g., `https://www.youtube.com/user/barbie`)

### Alternatives Considered

Adding a "Copy Channel ID" option on the Channel page (as is done by YouTube) and/or the video dropdown would mitigate the UX speedbump, to a decent extent.

### Issue Labels

ease of use improvement, improvement to existing feature

### Additional Information
Would have to research more to see how to achieve `#2` of that issue in a performant / simple way. IIRC, our current functions only allow searching channels by ID. If anyone has any ideas, please feel free to share.