Create mutation to support vulnerability state update

See Design Issue and parent Epic for details.

Implementation Plan

• backend create confirmVulnerability GraphQL mutation
  • replaces POST /api/:version/vulnerabilities/:id/confirm
  • Changes the state of the vulnerability to confirmed
• backend create resolveVulnerability GraphQL mutation
  • replaces POST /api/:version/vulnerabilities/:id/resolve
  • Changes the state of the vulnerability to resolved