[Doc] Improve ARM Lease Review Documentation and service teams' guidance

### Problem

The current ARM lease documentation explains what ARM leases are, https://github.com/Azure/azure-rest-api-specs/blob/main/.github/arm-leases/README.md, but it does not clearly describe the review process, what the lease-related labels mean, or what actions service teams should take when a PR is blocked by an ARM lease review.

### Proposal

Update the [PR flow documentation](https://aka.ms/azsdk/pr-diagram) at Azure SDK PR Review Flow and related ARM lease documentation to include:

- A clear explanation of ARM lease review labels and their meaning.
- The review workflow and decision process.
- The expected actions from service teams when a lease review is required.
- Contact points or escalation paths when additional help is needed.

Start with .github/arm-leases/README.md and review the linked Azure SDK PR Review Flow documentation. Identify the ARM lease labels, review workflow, service-team actions, and contact or escalation guidance described in the issue. Done means the relevant documentation clearly covers all four proposal points and is consistent across the linked materials.

Written by the indexing model from the issue text.