Add feature flag for service desk ticket type

What does this MR do and why?

This MR just adds the feature flag for service desk ticket for future issues.

Resolves #414529 (closed)

This is granular MR just in spirit of iteration.

See [Feature flag] Rollout of `service_desk_ticket` (#416343)

Screenshots or screen recordings

NA

How to set up and validate locally

NA

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.

Related to #414529 (closed)