Add optional support to create secret and shell for additional support

[KannanThiru]

- What I did

Added two optional release features:

• Post-deploy shell commands
• Kubernetes secret creation/management
• Extended release config support so each release can define:

Features:

• Run configured shell commands
• Improved secret handling to avoid double encoding:

If a secret value is already base64-encoded, it is kept as-is
Plain values are handled as plain text and encoded by Kubernetes as needed
Added documentation and examples in README for both features.

- Why I did it

Streamline cluster pipeline and simplify the process

- How to verify it

Added tests and fixture coverage for:

Config parsing of shell and secrets
Dry-run/diff-run skip behavior
Secret validation
Base64 detection logic
Overall impact:

Backward compatible (features are optional)
More flexible post-deploy automation
Better secret handling for mixed plaintext/base64 inputs

• Meme/emoji that summarize this change (not mandatory)