feat: add cf manifest command for external tool integration

[rkoster]

Summary

• Add ibosh cf manifest command that outputs the interpolated CF deployment manifest with all ops files applied
• Enables external tools to build on top of the ibosh-generated CF manifest
• Refactor CFDeployAction to use shared functions for DRY code

Features

• Variable credentials remain as placeholders (e.g. ((cf_admin_password))) since they are generated by config-server during deployment
• system_domain and router_static_ips are substituted with resolved values
• BOSH env is optional when --router-ip is explicitly provided
• Manifest output goes to stdout, info messages to stderr (enabling clean piping)

Usage Examples

# Auto-select router IP (requires BOSH env)
eval "$(ibosh docker print-env)"
ibosh cf manifest

# Use specific router IP (no BOSH env needed)
ibosh cf manifest --router-ip 10.245.0.34

# Use custom system domain
ibosh cf manifest --router-ip 10.245.0.34 --system-domain my.domain.com

# Save to file for external tools
ibosh cf manifest --router-ip 10.245.0.34 > manifest.yml

Changes

• internal/commands/cf.go: Added shared types (CFManifestConfig, CFManifestFiles) and functions (ResolveCFConfig, PrepareCFManifestFiles), new CFManifestAction, and refactored CFDeployAction
• cmd/ibosh/main.go: Registered new manifest subcommand under cf
• internal/commands/commands_test.go: Added test for CFManifestAction export