- added AzurePipelinesPool as a abstraction for vmImage and on prem p…

[mateuszradny]

I want to use nuke.build with our on-prem agents. Unfortunately, I didn't find a solution to pass a pool name to be considered in the final yml file.

I saw that other people also had a similar problem: #1173, #749.

My proposition is to create an additional abstraction, AzurePipelinesPool, which can be either a Microsoft-hosted agent (vmImage) or a self-hosted agent, as that is essentially what a pool is in Azure Pipelines.

Here is a proposal for the changes, and I am open to suggestions. I also removed images parameters from AzurePipelinesAttribute because if you really need to run your targets on multiple vmImages, it's probably better to configure multiple AzurePipelinesAttribute, am I right?

I confirm that the pull-request:

• [x] Follows the contribution guidelines
• [x] Is based on my own work
• [x] Is in compliance with my employer