Make dstull license backend maintainer

Overview

Overall GitLab experience: 1yr and 390+ MRs merged.

Projects maintainer on: Versions application with 170+ MRs merged and 70+ MRs reviewed/approved

License app:

• authored MRs
• considerable contributions to overall health and maintainability of the application through https://gitlab.com/gitlab-org/license-gitlab-com/-/issues/167

Developer checklist

• Before this MR is merged
  • Assign this issue to your manager
• After this MR is merged
  • Request a maintainer from the #license-gitlab-com Slack channel to add you as a Maintainer to https://gitlab.com/gitlab-org/license-gitlab-com

Manager checklist

• Before this MR is merged
  • The MR has been open for 5 working days
  • More than half of the existing maintainers approve the MR
  • There are no blocking concerns raised (if there are, please follow https://about.gitlab.com/handbook/engineering/workflow/code-review/#how-to-become-a-project-maintainer)
• After this MR is merged
  • Announce the good news in the relevant channels listed in https://about.gitlab.com/handbook/engineering/#keeping-yourself-informed

/cc @jameslopez @rdavila @asubramanian1 @tyleramos @shreyasagarwal