Ability to add more commands (rather than just `!drop`)

**Is your feature request related to a problem? Please describe.**
Right now, the extension only observes the `!drop` command. While we have the ability to add more commands in the code, there is no way in the UI to do so.

**Describe the solution you'd like**
A user should be able to configure the commands. I'm not sure if it should happen in the extension [Popup](https://github.com/AhsanAyaz/chrome-ext-restream-mate/blob/main/src/pages/Popup/index.tsx) itself, or if we should do it in the [Options Page](https://github.com/AhsanAyaz/chrome-ext-restream-mate/blob/main/src/pages/Options/index.html)

**Additional context**
This would require for us to identify a set of commands. For example:
- Drop a rocket on the screen using `!drop` in the message
- Show a meme gif on the screen `!gif `.
- Play a sound `!play `

The user should be able to add commands as something like:
```
{
type: "play",
url: "URL of sound file"
}
```
Or
```
{
type: "gif",
url: "URL of gif"
}
```

This could use the [`chrome.storage.sync`](https://developer.chrome.com/docs/extensions/reference/storage/#usage) to sync these settings across chrome browsers using the same google account.