`kctrl`: Users should be able to install package repos globally using the CLI

**Describe the problem/challenge you have**
`kctrl` should expose a flag that allows addition of PackageRepos to the global namespace

**Describe the solution you'd like**
A `--global` flag with `package repo add` command which installs the PackageRepo in the global ns.

**Acceptance Criteria**
- [ ] Flag should use namespace specified by configuration
- [ ] Flag installs package repo in global ns
- [ ] Tests

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