Handle error when passing an invalid URL to Jira integration

Summary

Gitlab throws a "Something went wrong at our end" with the following 500 error when entering a Jira API URL with a trailing slash and saving at the project level:

NoMethodError (undefined method `scheme' for nil:NilClass):

lib/gitlab/http.rb:24:in `perform_request'
lib/gitlab/jira/http_client.rb:39:in `public_send'
lib/gitlab/jira/http_client.rb:39:in `make_request'
lib/gitlab/jira/http_client.rb:13:in `request'

Looks related to 4e4acc94 where we changed the library from net::http to gitlab::http.

Proposal

Invalid URLs are common and should throw an "Invalid URL" error to the user.

Customer issue: https://gitlab.zendesk.com/agent/tickets/131306 (Internal use only)