Add a new DAG that verifies Jobset Uptime metrics

[yuna-tzeng]

Description

This changes introduces a new DAG that automates the process of creating a TPU v6e-16 node pool, launching a jobset, and monitoring the jobset uptime metric to ensure it behaves correctly. It also includes a negative test case to verify metric behavior over invalid time ranges.

Tests

GCP Composer name: tony-test (under GCP project: cloud-ml-auto-solutions)
GCP Composer version: 2.13.1

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run one-shot tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed.