Vuln Report: Fix Jira error handling

What does this MR do and why?

Vuln Report: Fix Jira error handling

When Jira integration is enabled and the connection to it fails, the Vulnerability Report shows an error alert and no data.

This MR fixes this and also displays the error message from the BE, which gives the user instructions on how to fix the problem.

Changelog: changed EE: true

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