Add Cluster Mode Support for Loki BOSH Release

[msawant060]

Currently, the loki-boshrelease deploys Loki in a single-instance mode. This setup is not suitable for production environments that require high availability (HA) and zero-downtime upgrades.

🔧 Feature Request:
Support for Loki in clustered mode with the following:

Stemcell update safety:
Rolling deploy without full service interruption.