Feat: add support for distributed serving type

[linnlh]

Purpose of this PR

This PR introduces a new serving type called distributed to Arena's serving module. The primary motivation behind these changes is to enable the deployment of large-scale models across multiple nodes within a Kubernetes (K8s) cluster.

Proposed changes:

• Introduce a new serving type called distributed to Arena's serving module which can deploy model across multiple nodes.
• Update the relevant doc to provide guidance for using distributed serving type.

Which issue(s) this PR fixes:
Fixes #1186

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

The distributed serving type addressed the increasing demand for multi-host inference due to the advancement of large language models (LLMs) such as Meta's Llama-3.1-405B. Currently, Arena lacks the capability to deploy models distributed across multiple nodes, and this PR aims to fill the gap.

[google-oss-prow]

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[linnlh]

@ChenYi015 @cheyang @Syulin7