New API Support: Project Aliases API
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## New API / Endpoint
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API documentation: https://docs.gitlab.com/api/project_aliases/
## Additional Details
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- [ ] I'd like to contribute it myself
## Implementation Guide
The code in `client-go` has a strong pattern that is repeatable when adding support for new APIs.
- Read the instructions in `CONTRIBUTING.md` to get your local development environment set up.
- Follow the instructions in `AddingAPISupport.md`.
- This file includes instructions for adding all endpoints of an API.
- It also describes how to write functions for each type of endpoint, so can be used for adding new endpoint support as well.
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