[RFE] Support pre-provisioning on Azure

## Current situation
Currently azure-init does not support Azure pre-provisioning.

## Impact

Lack of support for pre-provisioning will affect adoption as it does not allow the customer to benefit from better reliability and performance gained from Azure pre-provisioning service.

## Ideal future situation

Add support for Azure pre-provisioning.

## Additional information

Currently the agent does not support Azure pre-provisioning (PPS). Since PPS is not a customer-facing feature, there's no public documentation for it, unfortunately.
cloud-init started supporting Azure PPS since version 18.5. Here's the commit that started the support: [link](https://github.com/canonical/cloud-init/commit/c03bdd3d8ed762cada813c5e95a40b14d2047b57)
Other relevant commits as reference:
Network event detection support via netlink: [commit](https://github.com/canonical/cloud-init/commit/bf7917159dbb292c9fcdef82b004e0f5ecb32c16)
PPS v2 support via nic attach/detach: [commit](https://github.com/canonical/cloud-init/commit/a4d0feb050e32277a218e45bfb6a496d26ff46d0)

Start by studying the linked cloud-init commit for Azure PPS support, then compare the related netlink network-event and PPS v2 nic attach/detach commits. Clarify the Azure PPS behavior and project entry points before planning the change; done means azure-init supports Azure pre-provisioning reliably, with validation for the relevant provisioning and network events.

Written by the indexing model from the issue text.