Add dummy "Loading" notification before actual player notification is ready

[opusforlife2]

Checklist

• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I have read the FAQ and my problem isn't listed.
• I'm aware that this is a request for NewPipe itself and that requests for adding a new service need to be made at NewPipeExtractor.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

Before the actual media info is ready to load into the player media notification, the app should show a "Loading media" dummy notification if possible.

Why do you want this feature?

As of 0.26.0, the app creates an "Unknown - Unknown" notification that can stay for up to 10+ seconds, until it gets populated with the actual media info. This is especially noticeable when background playback is used without loading the video page first.

This is a very long duration to stay unresponsive, which can cause confusion for users, making them think something is wrong.

Additional information

Opened as per #10712 (comment).