add support for multiple request body types

[mnahkies]

It's possible to declare different request bodies for different content types.

Currently we simply use the first one that we find:

openapi-code-generator/packages/openapi-code-generator/src/typescript/common/typescript-common.ts

Lines 95 to 109 in 1ffdc52

	// todo support multiple request body types
	for (const [requestBodyContentType, definition] of Object.entries(requestBody.content)) {
	return {
	requestBodyContentType,
	requestBodyParameter: {
	name: "requestBody",
	description: requestBody.description,
	in: "body",
	required: requestBody.required,
	schema: definition.schema,
	allowEmptyValue: false,
	deprecated: false,
	},
	}
	}

At a minimum we should support:

• multipart/form-data
• application/octet-stream
• text/plain

Ideally we'd additionally support XML, but that might be left for it's own issue.