Add Hydra composition for GiGL configs

[kmontemayor2-sc]

Summary

• Add opt-in Hydra Defaults List composition for GbmlConfig and GiglResourceConfig.
• Use the primary local file’s parent directory as the Hydra config root.
• Preserve the existing loader behavior for YAML without defaults.
• Keep GCS and HTTP inputs limited to plain, single-file YAML; remote composition is not included.
• Have ConfigValidator resolve and materialize both task and resource configs using the pipeline identity.
• Route resolved config URIs and the GLT backend decision through ConfigValidator outputs.
• Disable ConfigValidator caching so fragment changes cannot reuse stale outputs.
• Refactor the E2E resource configs to use shared infrastructure and preprocessing fragments.

Validation

• make assert_yaml_configs_parse
• Hydra/protobuf unit tests: 17 passed
• ConfigValidator unit tests: 7 passed
• make type_check
• Ruff lint and Python format checks
• Markdown formatting checks
• Verified that all three refactored E2E configs retain their original protobuf fingerprints