feat: add full support for managing API keys

[mbevc1]

Following #937 backend has added GET /service-accounts/{org}/{name}/api-keys/{key_id} (Get an API key for a service account).

OpenAPI spec: https://app.kosli.com/api/v2/doc/#/Service%20Accounts/get_service_account_api_key

Aim is to expand kosli get to include api-key and complete full support of API keys CRUD operations. We also need to make sure to add testing and follow existing CLI patters.