Release expose_dismissal_reason feature

What does this MR do and why?

Release expose_dismissal_reason feature flag

Related to #416377 (closed)

High-level description: Vulnerability bulk status updates (&4649 - closed)

How to set up and validate locally

1. Make sure you have some Vulnerabilities in a project
2. Dismiss some of them with different reasons
3. Execute the following GraphQL query

query {
  project(fullPath: "<PROJECT PATH HERE>") {
    vulnerabilities(state: [<states here>], dismissalReason: [<DISMISSAL REASONS HERE>]) {
      nodes {
        id
        state
        dismissalReason
      }
    }
  }
}

4. dismissalReason should not be empty

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.