Add support for music.youtube.com

[mileswatson]

Description

Brave rewards tab only recognises the base URL "music.youtube.com" as "youtube.com". Any other path produces the "No activities yet" page on the Brave Rewards window. Furthermore, "https://youtube.com/results?q=example" also suffers from this issue.

Steps to Reproduce

1. Visit "https://music.youtube.com/hotlist", "https://music.youtube.com/library", or "https://music.youtube.com/search?q=example" URLs. This also occurs on "https://youtube.com/search?q=example".
2. Click on the brave rewards icon in the top right.

Actual result:

The Brave Rewards window will display the "No activities yet..." page.

Expected result:

It should recognise "youtube.com" as the domain, e.g. "youtube.com (?) Not yet verified" (like it is on "https://youtube.com")

Reproduces how often:

Easily Reproduced

Brave version (brave://version info)

Brave: 0.64.56 Chromium: 74.0.3729.75 (Official Build) dev (64-bit)
Revision: fdb7915642fef8cf997beac2554709d148e3c187-refs/branch-heads/3729@{#754}
OS: Windows 10 OS Build 17134.706

Version/Channel Information:

Tested on dev and nightly, possibly occurs on other channels.