[FEATURE REQ] Warn if multiple http client providers are on classpath.

[kasobol-msft]

Is your feature request related to a problem? Please describe.
When multiple http providers are on classpath it's unclear which is being picked up.
I.e. this code picks first one

azure-sdk-for-java/sdk/core/azure-core/src/main/java/com/azure/core/implementation/http/HttpClientProviders.java

Lines 15 to 29 in a564e07

	private static HttpClientProvider defaultProvider;
	private static final String CANNOT_FIND_HTTP_CLIENT = "A request was made to load the default HttpClient provider "
	+ "but one could not be found on the classpath. If you are using a dependency manager, consider including a "
	+ "dependency on azure-core-http-netty or azure-core-http-okhttp. Depending on your existing dependencies, you "
	+ "have the choice of Netty or OkHttp implementations. Additionally, refer to "
	+ "https://aka.ms/azsdk/java/docs/custom-httpclient to learn about writing your own implementation.";
	static {
	ServiceLoader<HttpClientProvider> serviceLoader = ServiceLoader.load(HttpClientProvider.class);
	// Use the first provider found in the service loader iterator.
	Iterator<HttpClientProvider> it = serviceLoader.iterator();
	if (it.hasNext()) {
	defaultProvider = it.next();
	}
	}

Describe the solution you'd like
The HttpClientProviders should either throw runtime exception (and fail fast) or at least log warnings enumerating providers being on classpatch and printing one that has been chosen.
Maybe we should consider some priority list to decide which is picked if multiple are present to make it more predictable.

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