refactor: cleanup and implementation

CHANGELOG.md

spec/endpoints/applications/index.yml

spec/endpoints/attachments/uuid.yml

spec/endpoints/destinations/index.yml

spec/endpoints/destinations/uuid.yml

spec/examples/application-state.yml

spec/examples/application.yml

spec/examples/create-application.yml

spec/examples/create-destination.yml

spec/examples/destination-list.yml

spec/examples/destination.yml

spec/examples/update-destination.yml

spec/headers/cache-control-no-cache.yml

spec/parameters/documentId.yml

spec/schemas/application-schema.yml

spec/schemas/application.yml

spec/schemas/attachment.yml

spec/schemas/create-application.yml

spec/schemas/create-attachment.yml

spec/schemas/create-destination.yml