Describe the feature or problem you’d like to solve

Codespaces supports secrets that can be set on a user's account and shared with multiple repositories, similar to Actions organization secrets.

https://docs.github.com/en/codespaces/managing-your-codespaces/managing-encrypted-secrets-for-your-codespaces

There is currently only API support for user-secrets, which requires the user scope
https://docs.github.com/en/rest/reference/codespaces#secrets

Proposed solution

We should support managing Codespaces user secrets via the CLI similar to how Actions secrets are managed.