Use provide/inject for vulnerabilities export endpoint

What does this MR do?

On the vulnerability report, there is an Export button that exports the vulnerabilities to a CSV:

This button needs a vulnerabilitiesExportEndpoint URL that's provided by the backend. The component tree looks like this:

We have 3 dashboard levels, and vulnerability_report_init.js will render one of the 3 *_security_dashboard.vue components. Previously, the URL was passed down to the security_dashboard.vue component as a prop, then again to csv_export_button.vue as a prop. However, the security_dashboard.vue component doesn't use it, it just passes it down. This MR simplifies the code by changing it to use provide/inject instead.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• [-] 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.
• [x ] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #324246