How to add MulanPSL-2.0 license to LICENSE template
### Proposal
_This was originally proposed in #369444 by @qk44077907 (a member of @gitlab-jh) in 2022-08._ _EDITED BY @tnir in 2022-08._
The license template list does not contain the `MulanPSL-2.0` license (as of %15.4), and a user needs to copy and paste rawly to the project if they want to specify MulanPSL-2.0 (`MulanPSL-2.0`).

### Goal
1. Make `MulanPSL-2.0` appear on the default license template list on `SaaS` (~"GitLab Free", ~"GitLab Premium", or ~"GitLab Ultimate").
1. Make `MulanPSL-2.0` appear on the default license template list on "self-managed" (~"GitLab Free" or ~"GitLab Premium").
- ~SaaS
- ~"self-managed"
### References
- In ~"GitLab Ultimate" on ~"self-managed", they can use the feature: https://docs.gitlab.com/ee/user/admin_area/custom_project_templates.html
issue