Request validation incorrectly treats optional requestBody as required when only one content type is defined

[dgmora]

The request body validator schema ignores the requestBody.required field from the OpenAPI spec. Instead, it treats the request body as required whenever there is exactly one content type defined:

openapi-backend/src/validation.ts

Lines 581 to 584 in 55aa296

	if (_.keys(requestBody.content).length === 1) {
	// if application/json is the only specified format, it's required
	requestBodySchema.required.push('requestBody');
	}

Per the https://swagger.io/docs/specification/v3_0/describing-request-body/describing-request-body/, requestBody.required defaults to false. The number of content types should not determine whether the body is required. Is there a reason for this difference? Thanks!

[dgmora]

This is actually a dup of #292, that one didn't receive any feedback.