Ensure proper validation for GIT url is performed for all requests

!72323 (merged) introduced url validation for GIT imports, but according to #340435 (comment 732328082) we are still receiving errors, coming from Git validation

I've identified two sources of problem:

• it is possible to bypass validation by pasting URL and hitting Enter without blurring field
• there is another form (importing repository when you create project without repository and after that initialize a repository inside project via import)

We need to bring consistency of validation across all the GitLab