Resolve "WebHookService doesn't handle user info with nil passwords"

What does this MR do?

Provides a fallback ('') for missing passwords in the webhook url.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them

What are the relevant issue numbers?

Closes #46571 (closed)