Move pages selectors into metadata.json

[dabreadman]

Is your feature request related to a problem?

Seeing we have metadata.json for players, we could do the same for pages, which makes it easier for contribution and separation of concern.

Describe the solution you'd like

Have it structured as such,

getIdentifier(): string {
    return new Function(metadata.getIdentifier.arguments, metadata.getIdentier.body)()
  }

### Describe alternatives you've considered

_No response_

### Additional context

Example Metadata
```json
{
     "pageUrls": ["*://beta.crunchyroll.com/*"],
     "selectorStrings": {
         "default": { // do we even need this :?
            "getIdentifier":{
                  "arguments": "",
                  "body": "return window.location.pathname.split('/')[2]" // <- wonder if reference gonna be right :U
                                                                          // guess we could simply pass in the window object
                  }
            ...
         }
     }
}

Function serialization/deserialization
https://stackoverflow.com/questions/36517173/how-to-store-a-javascript-function-in-json

Code of Conduct

• I agree to fill in the correct information

[lexesj]

Due to CSP issues this one might not be possible.