feat(codegen): generate empty SdkWarmUpProvider and META-INF/services registration per service

[joviegas]

Motivation and Context

This change makes codegen emit a provider plus its ServiceLoader registration in every service module. The warmUp() body is empty in this PR; the synthetic priming call is added in a follow-up PR.

Modifications

• WarmUpProviderSpec: generates <Service>WarmUpProvider in <service>.internal.crac, implementing SdkWarmUpProvider with an empty warmUp().
• WarmUpProviderRegistrationTask: writes the provider's class name into META-INF/services/software.amazon.awssdk.core.crac.SdkWarmUpProvider. Creates the file once, appends per service, skips duplicates.
• WarmUpProviderTasks: emits both outputs, wired into AwsGeneratorTasks so every service runs it.
• Metadata.getFullCracInternalPackageName() and GeneratorPathProvider.getWarmUpProviderDirectory(): resolve the package and output directory.

Testing

• Added Junits in codegen
• Will add test in codegen-generated-classes-test after Part B that is implementation of actual wampUp api for each services is completed.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

License

• I confirm that this pull request can be released under the Apache 2 license