feat: add package scan command for PackageRepository

[timmilesdw]

Added d8 system package scan <repository-name> command that creates a PackageRepositoryOperation CR to trigger a full scan.

Usage:

• d8 system package scan my-repo
• d8 system package scan my-repo --timeout 10m
• d8 system package scan my-repo --name custom-name
• d8 system package scan my-repo --dry-run

Features:

• Validates PackageRepository exists before creating operation
• Shell tab-completion for repository names
• --dry-run to preview without creating
• Auto-generated name with manual marker and nanosecond timestamp
• deckhouse.io/created-by: deckhouse-cli annotation
• Unit tests included