[Key Vault] az keyvault ekm-connection: Add private endpoint support

[Yash (notyashhh)]

Related command
az keyvault ekm-connection private-endpoint
az keyvault ekm-connection create/update --connectivity-mode

Description
Adds EKM private endpoint create, delete, show, list, wait, and operation-status commands. Adds --connectivity-mode to connection create/update, preserving private endpoint names without appending a port and keeping the existing mode when omitted.

Uses API 2026-07-01-preview and azure-keyvault-administration 4.8.0b3. Create/delete support --no-wait; synchronous operations use ARMPolling to handle the private SDK’s Azure-AsyncOperation header.

Related to Azure/CLIPS#606 (CLI portion) and ADO task 37775795. No new preview labels are added. Removal of the existing parent EKM preview label is handled separately in #34095, which should land first.

Before merge
This is a draft pending the public SDK package. 4.8.0b3 is currently a private wheel, not available on PyPI, so clean dependency installation remains blocked. The wheel is not included in this PR. We need to compare the public package with this build, update the pins if needed, and rerun validation. Command naming also needs confirmation against the ADO request.

Testing Guide

• 30 EKM tests passed, including CLI request serialization, public/private mode handling, polling failures, and --no-wait.
• Key Vault pylint, flake8, and command lint passed. Help checked with the GA changes from [Key Vault] az keyvault ekm-connection: Remove preview status #34095 applied in memory.
• Live-tested a temporary endpoint: create, show, list, wait, operation status, and delete all passed. Verified that the original HSM connection, existing endpoint, and PLS connections were unchanged after cleanup, excluding audit history and ARM etags.
• Live reads and approval waits passed for the existing private endpoint. Switching the active EKM connection and traffic through the temporary endpoint were not tested, to avoid disrupting the shared HSM. Documentation generation was not run locally.

History Notes
[Key Vault] az keyvault ekm-connection private-endpoint: Add commands to manage EKM private endpoints and inspect operation status
[Key Vault] az keyvault ekm-connection create/update: Add --connectivity-mode to select public or private endpoint connectivity

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[azure-client-tools-bot-prd]

Hi Yash (@notyashhh),
Since the current milestone time is less than 7 days, this pr will be reviewed in the next milestone.

[Yong Zhang (yonzhan)]

Thank you for your contribution! We will review the pull request and get back to you soon.