add support for YouTube channel links when setting embeds

[SP4CEBARsystems]

1. Add support to detect links like youtube.com/@sp4cebar to the URL interpreter and extract the @handle, both can be done with a single regex (separate from the existing one)

const regex = /^https?:\/\/(?:www\.)?youtube\.com\/@([A-Za-z0-9._-]+)\/?$/;

const url = "https://youtube.com/@sp4cebar";
const match = url.match(regex);

if (match) {
    console.log(match[1]); // sp4cebar
}

2. Use the YouTube API to get the channel ID: https://www.googleapis.com/youtube/v3/channels?part=snippet&forHandle=@veritasium&key=API_KEY
3. Given a channel ID like mine below, you can change the initial UC to UU and create a link to a playlist with all videos uploaded to this channel as shown below as well.
   • my channel ID: UCNtSJKxSW7GsohL8g3aN_Zg
   • my channel playlist: https://m.youtube.com/playlist?list=UUNtSJKxSW7GsohL8g3aN_Zg
   • Notice the IDs starting with UC and UU