feat: complete volume purchasing location support

[neilmartin83]

Change

Thank you for your contribution !

Flesh out support for managing volume purchasing locations, so CRUD is now working for them via the SDK. I also have an incoming PR for a new Terraform provider resource that works with these changes.

Please note this depends on the following PR being accepted first, so that updates (PATCH requests) work: deploymenttheory/go-api-http-client-integrations#12

Type of Change

Please DELETE options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update (Wiki)
• Refactor (refactoring code, removing code, changing code structure)

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (readme)
• I did format my code