Extract channel routes (#2227)

* Extract primary channel routes from invidious.cr

Also removes timedtext_video stub since all it does is redirect to the
homepage. However, Invidious's 404 handler already does this.

--
As the template for the channel about page doesn't exist yet, the
behavior for the /channel/:ucid/about endpoint has been changed to be
the same as what's currently present on Invidious

(cherry picked from commit 8fad19d8057d7d22e3de27ebbc88a9978c1df27b)

* Manually extract brand_redirect from 1b569bbc99207cae7c20aa285f42477ae361dd30

This commit manually extracts the brand_redirect function from the
commit mentioned.

However, the redirect to the  `.../about` endpoint is removed due to the
fact that it doesn't exist yet.

This commit is also mainly just a bridge for the next few cherry picks from
\#2215

* Update brand_redirect to use youtubei resolve_url

(cherry picked from commit 53335fe7cfdfac392365b7cac447bc7cc6478134)

* Add additional channel endpoints to brand_redirect

(cherry picked from commit 8fc6f3add637dabb09b2034f4d82fc3d039ba15c)

* Add separate handler for /profile endpoint

* Add /channel/:ucid/home route

* Document all channel brand_urls

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