Draft: Added table and model for storing vulnerability resolution data

What does this MR do and why?

This MR adds a new table vulnerability_resolutions to store the relationship between the vulnerability finding and corresponding ai workflow for its resolution. This is as per https://gitlab.com/gitlab-org/gitlab/-/issues/570181#implementation-plan.

References

https://gitlab.com/gitlab-org/gitlab/-/issues/570181#implementation-plan

How to set up and validate locally

Since only a table and model is added, it can be tested by running rspecs.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #570181