refactor(managedclusters): extract helper methods from Parameters()

Split the monolithic Parameters() method (340 lines, complexity 55) into
focused helper methods to improve readability and maintainability.

Extracted methods:
- convertExistingToHub: convert existing object to hub version
- initializeManagedCluster: create or return existing cluster
- configureBasicProperties: set name, owner, identity, location
- configureNetworkProfile: network settings and CIDR configuration
- configureServiceCIDR: service CIDR and DNS IP calculation
- configureLinuxProfile: SSH and Linux settings
- configureOperatorSpec: kubeconfig secrets configuration
- configureAADProfile: Azure Active Directory settings
- configureAddonProfiles: add-on configuration
- configureSKU: SKU tier settings
- configureAPIServerAccessProfile: API server access settings
- configureIdentity: identity and kubelet identity
- configureHTTPProxyConfig: HTTP proxy settings
- configureOIDCIssuerProfile: OIDC issuer settings
- configureAutoUpgradeProfile: auto upgrade settings
- configureSecurityProfile: security profile orchestration
- configureAgentPoolProfiles: agent pool configuration
- convertToTargetVersion: convert to stable/preview API

Also extracted constants for magic strings (identityTypeMSI, dnsIPLastOctet).

No functional changes - all existing tests pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>
Co-Authored-By: Bryan Cox <[email protected]>

Author: bryan-cox