Add Threads entry and "xmt" rule

[rileychh]

Removes the xmt tracking parameter from Threads share links.

Example

Before:
https://www.threads.com/@ntut.uk/post/DWMXR8hkvbI?xmt=AQF0X5xurim8xkCkUa9dIycDta4luuIZx-jFf80eaQqd0Q

After:
https://www.threads.com/@ntut.uk/post/DWMXR8hkvbI

[AkitsukiNagi]

I reviewed your PR and found a structural issue in the JSON file:

The provider "threads" should be a key within "providers". However, it is sibling to it currently.

Current:

{
    "providers": {
        ...( the others)
        "viglink.com": {
            ...(VigLink rules)
        }
    },
    "threads": {
        ... (Threads rules)
    }
}

Corrected:

{
    "providers": {
        ...(the others)
        "viglink.com": {
            ...(VigLink rules)
        },
        "threads": {
            ...(Threads rules)
        }
    }
}

Tip

You may change the provider name to "threads.net" as most providers are named so.

[rileychh]

Thanks @AkitsukiNagi, fixed and force-pushed. Also rebased onto latest master and added an example URL to the PR body.

Kept the key as "threads" since bare-name keys are common in the file. Can rename to "threads.com" if you prefer (the pattern matches .com, not .net).