Support alternative servers in PathItems and Operations

[charjr]

Currently alternative servers are only supported if you use cached builders.

Building processors on the fly with ResponseBuilder and RequestBuilder currently only support Root level servers:

membrane-core/src/OpenAPI/Builder/RequestBuilder.php

Lines 58 to 60 in 9c536a2

	private function matchServer(Cebe\OpenApi $openAPI, string $url): string
	{
	$servers = $openAPI->servers;

membrane-core/src/OpenAPI/Builder/ResponseBuilder.php

Lines 82 to 84 in 9c536a2

	private function matchServer(Cebe\OpenApi $openAPI, string $url): string
	{
	$servers = $openAPI->servers;

We currently match servers first, which means we do not know which path or operation to take servers from.