Hashtag API: Parse header when getting the first page

[ChunkyProgrammer]

When requesting the first page of a hashtag (without continuations), YouTube will include a hashtag header that includes info such as the # of videos and # of channels in the hashtag.

This PR will parse those properties (it also creates separate structs for the hashtag page + header)

Before

{
  "results": [
    {
      "type": "video",
      ...
    }
  ]
}

After

Page 1:

{
  "type": "hashtagPage",
  "header": {
    "type": "hashtag",
    "title": "#cat",
    "url": "/hashtag/cat",
    "channelCount": 8100000,
    "videoCount": 1100000
  },
  "results": [
    {
      "type": "video",
      ...
    }
  ],
  "hasNextPage": true
}

Page 2:

{
  "type": "hashtagPage",
  "results": [
    {
      "type": "video",
      ...
    }
  ],
  "hasNextPage": true
}

[SamantazFox]

Are these infos really useful? The numbers looks very approximated.

[ChunkyProgrammer]

Are these infos really useful? The numbers looks very approximated.

It was mentioned in my PR to add hashtag pags to FreeTube FreeTubeApp/FreeTube#3483 (comment)

@efb4f5ff-1298-471a-8973-3d47447115dc any thoughts on this?

[efb4f5ff-1298-471a-8973-3d47447115dc]

Sorry for the delay. So i mentioned the possibility to add this because with the stats the user knows what they are getting into. A hashtag with low amount of approximate videos could make the user go through all of them and a high amount can make the user refrain from watching too much and falling into hours of watching videos.

[SamantazFox]

Ah, I see, thanks!

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[ChunkyProgrammer]

Updated and working again