ci: new VHD pipeline definition for Ubuntu + gen2 images

[jackfrancis]

Reason for Change:

This PR adds a new Azure DevOps pipeline spec for building Generation 2 Ubuntu VHDs.

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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[codecov]

Codecov Report

Merging #2958 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2958   +/-   ##
=======================================
  Coverage   72.57%   72.57%           
=======================================
  Files         141      141           
  Lines       25934    25934           
=======================================
  Hits        18821    18821           
  Misses       6014     6014           
  Partials     1099     1099