Adding support for self-hosted pools

[kuqin12]

This change added support for self-hosted agent pools for potentially onboarding Windows on ARM systems as there is no plan for Microsoft hosted Windows ARM agents as of today.

The main change is around the flag of installing tools or not. The existing routine will expect the incoming flag being a boolean type, which does not work when this parameter is being populated using a variable (string). This change will update the flag to string type as well.

After changing, the only file being synced to individual repos is MuDevOpsWrapper.yml. And each repo can configure their own build matrix for build target, architecture list, run on selfhost agents or not, etc.

This is considered a breaking change, due to:

1. Steps/PrGate.yml updated the extra_install_steps to be invoked before stuart_setup and stuart_update. But this change does not knowingly break the existing consumers.
2. Jobs/PrGate.yml updated the parameters to accept parameters.build_matrix, which needs the consumers to update top level yaml script to comply with the updated template.

[kuqin12]

For reference, the PRs that integrate this change for mu repos are: https://github.com/microsoft/mu_basecore/pull/404 https://github.com/microsoft/mu_oem_sample/pull/85 https://github.com/microsoft/mu_plus/pull/240 https://github.com/microsoft/mu_tiano_plus/pull/134 https://github.com/microsoft/mu_feature_config/pull/180 https://github.com/microsoft/mu_silicon_arm_tiano/pull/106 https://github.com/microsoft/mu_feature_ipmi/pull/118 https://github.com/microsoft/mu_tiano_platforms/pull/546 https://github.com/microsoft/mu_silicon_intel_tiano/pull/91 https://github.com/microsoft/mu_feature_dfci/pull/103 https://github.com/microsoft/mu_feature_mm_supv/pull/123 https://github.com/microsoft/mu_common_intel_min_platform/pull/149

[makubacki]

I will look at this in detail on Tuesday.