`java_toolchain` should support specifying a toolchain URL via OS architecture

[weaversam8]

I'm new to Please, but looking at the source code, it appears that java_toolchain only checks CONFIG.OS and does not check CONFIG.ARCH:

java-rules/build_defs/java.build_defs

Lines 571 to 582 in 55cf68c

	if not jdk:
	jdk_url = jdk_url if isinstance(jdk_url, str) else jdk_url.get(CONFIG.OS)
	if not jdk_url:
	fail(f"No jdk_url defined for platform {CONFIG.OS}")
	jdk = remote_file(
	name=f"_{name}#download",
	url = jdk_url,
	visibility = visibility,
	hashes = hashes,
	)

As of right now, that forces developers to either work around this in user code or fork this plugin.