Custom URI schemes don't function in embeds when used with hyperlink markdown

[JackTheFoxOtter]

Many applications and games use custom URI schemes to allow linking in-game content, joining sessions or calling certain actions.
From my testing however, when adding a link to an embed created by a bot account, only http:// and https:// protocols are actually carried over into the href property of the message, I could not get other URI protocols working.

Therefore I'm suggesting adding support for custom URI schemes, which would be rather simple to implement (simply allow any protocol to be used as a href instead of only http and https) but have a wide variety of uses for bot creators.

For security reasons, there should be a confirmation dialog similar to the one that pops up when you're accessing external websites, together with a "always trust this URI scheme" button for comfort of use on your favorite games / applications.

EDIT:
Turns out, all of the functionality above already works with normal links. What is isn't working with is using it with hyperlink markdown.

Adding <calculator://.> to the description of a markdown produces the following, working result:

However, adding [Calculator](<calculator://.>) doesn't produce a clickable hyperlink:

Considering everything I requested above is already implemented, it should be a rather straight forward thing to also make this compatible with hyperlink markdown.