[JENKINS-71391] always validate fields

[mawinter69]

currently validation of the fields happens only for on the global configuration page of Jenkins. With this change validation will happen also when configuring links on folders, projects and computers.

See JENKINS-71391

Testing done

Manually tested

Submitter checklist

• [x] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did
• [x] Link to relevant issues in GitHub or Jira
• [ ] Link to relevant pull requests, esp. upstream and downstream changes
• [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue