Generalize processing Lambda buildspec for mission deploys

[jamesray]

Summary

• Generalizes the processing Lambda CodeBuild buildspec around MISSION_NAME.
• Keeps HERMES as the default behavior while allowing mission-specific ECR repo names, base images, and requirements files.
• Passes MISSION_NAME, LAMBDA_PIPELINE=PROCESSING, and the image tag into the architecture build so deployments can be driven automatically again.

Why

The processing buildspec was tied to the original HERMES Lambda image and deployment project. This change makes the buildspec mission-aware while preserving the default HERMES path.

Validation

• Parsed buildspec.yml as YAML with Ruby.
• Ran git diff --check.
• Confirmed the Dockerfile accepts BASE_IMAGE and REQUIREMENTS_FILE build args.
• Scanned the changed file for high-confidence credentials; no AWS keys, GitHub tokens, Slack tokens, or private keys found.