Fix return types for backend resource deletions

[kylekz]

Description

When deleting resources, for example an Organization, the backend client is typed to return Organization, whereas the actual HTTP API returns a DeletedObject, resulting in a type mismatch. This PR:

• updates DeletedObjectJSON to accept a generic that extends string, with a default of string
  • i initially wanted this to extend ObjectType but then that would break DeletedObject.fromJSON()
• changes the generics passed into this.request() for the following resource delete methods:
  • Allowlist
  • Domain
  • EmailAddress
  • Organization
  • PhoneNumber
  • RedirectUrl
  • SamlConnection
    • for this one i'm just assuming ObjectType.SamlAccount is the correct type, as there's no SamlConnection
  • User

I'm not sure what the convention would be for handling this DeletedObjectJSON type property so this just seemed like the most straight forward way that wouldn't break anything 😅

Checklist

• [x] npm test runs as expected.
• [x] npm run build runs as expected.
• [ ] (If applicable) JSDoc comments have been added or updated for any package exports
• [ ] (If applicable) Documentation has been updated

Type of change

• [x] 🐛 Bug fix
• [ ] 🌟 New feature
• [ ] 🔨 Breaking change
• [ ] 📖 Refactoring / dependency upgrade / documentation
• [ ] other: