FIX: Allow additional valid theme .git url formats (#12385)

Some git repos have a different ssh url scheme than github and we should
support them.

This change updates our regex format to account for repos that don't
start with "git", but are still valid ssh urls.

Also I added some tests to account for the various formats and to ensure
we don't show the public key when using https urls.

See: https://meta.discourse.org/t/182668

app/assets/javascripts/admin/addon/controllers/modals/admin-install-theme.js

@@ -24,7 +24,7 @@ export default Controller.extend(ModalFunctionality, {
   keyGenUrl: "/admin/themes/generate_key_pair",
   importUrl: "/admin/themes/import",
   recordType: "theme",
-  checkPrivate: match("uploadUrl", /^git/),
+  checkPrivate: match("uploadUrl", /^.*[@].*[:].*\.git$/),
   localFile: null,
   uploadUrl: null,
   uploadName: null,