feat: add MULTUS configuration mode support

[rollandf]

Add support for MULTUS configuration mode as an alternative to the existing STANDALONE mode. This allows the driver to integrate with Multus CNI for network configuration instead of managing network setup directly through NRI.

Changes:

• Add ConfigurationMode flag (STANDALONE/MULTUS) to driver configuration
• Conditionally disable NRI plugin initialization in MULTUS mode
• Skip NetAttachDef fetching and interface name generation when using MULTUS
• Use default VfConfig when no explicit config is provided
• Add plugin registration wait to ensure kubelet plugin is ready before publishing resources
• Update Helm chart to expose configurationMode parameter
• Add three new demo examples for Multus integration:
  • Single VF with Multus
  • Multiple VFs with Multus
  • Multiple ResourceClaims with Multus

In MULTUS mode:

• NRI plugin is disabled (Multus handles network attachment)
• NetAttachDef configuration is skipped
• Interface naming is delegated to Multus

In STANDALONE mode (default):

• Behavior remains unchanged
• NRI plugin manages network configuration
• Driver generates interface names and fetches NetAttachDef configs