Show error when Jira did not return any projects

What does this MR do?

This MR adds validation for page where Jira import is being started. In case Jira doesn't return any projects the page only shows an error message.

The reason for that might be wrong configuration (incl. permissions) on Jira side or no projects created in Jira.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done