Create and style the vulnerability status badge

What does this MR do?

For reference:

This MR does the following:

1. The status badge was converted from a static element in haml to a Vue component using GlBadge. This is so that when the vulnerability status is changed through the dropdown, the status badge text and color is updated client-side instead of needing a full page reload.

2. The page no longer does a full reload when the vulnerability state changes. It's handled through an AJAX call and updated client-side using the response.

3. A bug in the status changer dropdown was fixed that prevented it from updating itself when the vulnerability status was changed client-side. Tests have been added to cover this case.

4. The status text was moved from haml into Vue because it's difficult to have static haml content in between two Vue components without having to either use workarounds or create two Vue apps, one for each component.

Screenshots

Badge and dropdown update client-side

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (Feature is behind feature flag)
• [-] 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