Use vmImage in yaml and merge build definitions into 1 by using jobs. Disable all AppVeyor images except for WMF4. Disable flaky UseCompatibleCommand tests on Ubuntu in CI

[bergmeister]

PR Summary

• Use vmImage in yaml to merge all build definitions into 1 PSScriptAnalyzer-CI build definition by using jobs instead of defining the image in the build definition itself. This means the Ubuntu/macOs/Windows specific build definitions can be deleted after this PR. This reduces maintenance in Azure DevOps and makes it easier for us adapt for upcoming image changes. With that we now also test against both Ubuntu versions and using jobs prepares us for using multi-stage pipelines as the next step (there isn't really a benefit in terms of time-savings though). In a PR the individual stages are reported individually but I don't think we can have badges for the individual jobs.
• Since Azure DevOps seems to work fine, we can disable the other images in AppVeyor except for WMF4, for which Azure Pipelines does not have a hosted image for
• The sporadic failures in the UseCompatibleCommand test suite change over time, therefore disabling the test cases individually was not working well.
• Add build badge

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
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