Refactor APIs to return response body instead of ResponseEntity

[quaff]

It seems that all API call result is used for getBody() only, for example:

spring-ai/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiChatModel.java

Lines 199 to 202 in db9ac2f

	ResponseEntity<ChatCompletion> completionEntity = this.retryTemplate
	.execute(ctx -> this.openAiApi.chatCompletionEntity(request, getAdditionalHttpHeaders(prompt)));
	var chatCompletion = completionEntity.getBody();

I think it's better to return domain object directly instead of spring-web API, make it be parity to method parameters, like ChromaApi does:

spring-ai/vector-stores/spring-ai-chroma-store/src/main/java/org/springframework/ai/chroma/vectorstore/ChromaApi.java

Lines 128 to 137 in db9ac2f

	public Tenant getTenant(String tenantName) {
	try {
	return this.restClient.get()
	.uri("/api/v2/tenants/{tenant_name}", tenantName)
	.headers(this::httpHeaders)
	.retrieve()
	.toEntity(Tenant.class)
	.getBody();
	}

CAUTION: It's breaking changes.