Docker - KSM based authentication support (#1598)

[sdubey-ks]

Add KSM support & Optimize Docker Build

Summary

Adds Keeper Secrets Manager (KSM) based config.json retrieval for Docker deployments and optimizes builds with a comprehensive .dockerignore.

Authentication Mechanisms

1. KSM Token – one-time KSM token used for config.json retrieval from Vault.
2. KSM Config File – mounted KSM config used for config.json retrieval from Vault.
3. User/Password Flow
4. Unified Hierarchy – priority order: KSM-Config → KSM-Token → Config File Volume Mount → User/Password

Key Changes

• docker-entrypoint.sh: Added KSM based config json retrieval methods.
• keepercommander/service/README.md: Updated docker deploy section for all authentication methods.
• .dockerignore: Created to exclude build artifacts, tests, virtualenvs, dev tools, docs, logs, and temp files to reduce context size.