Show loader and disable buttons when posting an issue

Summary

When submitting an issue report, a spinner should be displayed and the submit buttons should be disabled to prevent double posting, as the operation is slow due to communication with the Gitea API.

Steps to Reproduce

Not provided.

Expected Behaviour

A spinner is shown and buttons are disabled while the issue is being posted.

Actual Behaviour

No spinner is shown and buttons remain active, allowing double posting.

Environment

Not provided.

Reported by retoor via DevPlace.