Replace AskVAApi AMS serializers with JSONAPI serializers

[stevenjcumming]

Summary

Replace ActiveModelSerializers (AMS) with JSON:API Serializers in modules/ask_va_api.

Epic

• https://github.com/department-of-veterans-affairs/va.gov-team/issues/83609

Tasks

• [x] Replace serializer (1x)

Acceptance Criteria

• [x] Each serializer uses jsonapi-serializer
• [x] Each serializer has 100% coverage

[ericboehs]

Closing as a dupe of https://github.com/department-of-veterans-affairs/va.gov-team/issues/83609

[stevenjcumming]

Reopened because this is for a specific module, the title of the ticket is misleading