Cannot use : character in username

[jrohel]

Same problem in DNF5 rpm-software-management/dnf5#1556. Because both projects use librepo.
Librepo uses libcurl. To set the username and password librepo uses the old libcurl API option CURLOPT_USERPWD.

Suggested fix:
Extend librepo API. The new librepo API will use the new libcurl API options CURLOPT_USERNAME and CURLOPT_PASSWORD.
Modify dnf5 to use the new librepo API.