feat: add subscriptionId template parameter to E2E pipeline

[rchincha]

Adds an optional subscriptionId parameter to e2e-template.yaml so the orchestrator can override which subscription E2E tests run against. Defaults to the variable group value, so existing callers are unaffected.

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

[Copilot]

Pull request overview

Adds an optional subscriptionId template parameter to the Azure DevOps E2E pipeline template so an orchestrator pipeline can override which subscription E2E tests target, while preserving the existing default behavior (via $(E2E_SUBSCRIPTION_ID) from the variable group).

Changes:

• Introduced a new subscriptionId parameter with a default of $(E2E_SUBSCRIPTION_ID).
• Wired the AzureCLI task environment variable E2E_SUBSCRIPTION_ID to use the new parameter value.

[aks-node-assistant]

AgentBaker Linux gate detective

Run: https://msazure.visualstudio.com/CloudNativeCompute/_build/results?buildId=168753882
Failed job/stage/task: $(System.Collections.Hashtable.job)
First failing step/test: $(System.Collections.Hashtable.first)

RCA: E2E infrastructure flake: VMSS was created on shared cluster abe2e-kubenet-v5-150ee, but Azure Bastion SSH handshake timed out 5/5 times before validation/log collection. Not PR-caused from current evidence.

Confidence: High for the primary signature. Corroborated by timeline/status, focused failed logs, associated changes, and the flakiness wiki before publishing.

Strongest alternative: subscriptionId template parameter routed to wrong place; less likely because VMSS was created on expected shared cluster and failure is specifically Bastion SSH handshake.

Recommended owner/action: AgentBaker E2E test-infra: inspect Bastion health and shared-cluster network reachability.

Wiki signature: $(System.Collections.Hashtable.sig) (source of truth)