feat: add remaining database configuration cluster update

[Davidonium]

• Add database configuration parameters to the cluster update command: --replication-factor, --write-consistency-factor, --restart-mode, --rebalance-strategy, and --optimizer-indexing-threshold
• Shell completions for --restart-mode and --rebalance-strategy flags with valid values
• Confirmation prompt showing a diff of old vs new values before applying changes (skippable with --force)
• Move shared formatting utilities (DiffValue, OptionalValue) to the output package for reuse across commands.

The cluster update command previously only supported updating labels. This PR extends it to support modifying database configuration fields via the Qdrant Cloud API. Each flag is independently optional, and only changed fields are included in the update request.

A confirmation prompt displays the current and proposed values in an old => new format before proceeding, consistent with the existing cluster scale command UX. The --force flag bypasses the prompt for scripting use cases.

The scaleDiff helper was generalized into output.DiffValue and moved to the output package, replacing the local copy in scale.go.