Clean up vulnerability findings actions

What does this MR do?

• Replaces group with vulnerable in VulnerabilityFindingsHistory. This will allow it to be reused by controllers related to the instance security dashboard.
• Fix vulnerability findings summary spec. It was passing, and shouldn't have been.
• Extract #filter_params into controllers. It was defined in VulnerabilityFindingsActions but also used in VulnerabilityFindingsHistory. This created an unintentional coupling between the modules.

Preliminary work for #33899 (closed)

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #33899 (closed)