When a PR is made into HLD, write the generated manifests into PR description / comment

[samiyaakhtar]

This is a very useful feature to have and helps validate if the PR should be approved or not. A developer looking at the PR should be able to see generated manifests (using fabrikate) with the changes being requested to merge.

Note: This feature might require work in the bedrock-cli repo, and this work was done for the gitlab repos - https://github.com/microsoft/bedrock/blob/master/gitops/gitlab/.ci/diff.sh