Epic: Support optional SDK workload templates

[genalt]

Workloads overview spec

This Epic tracks the work needed for the Template Engine to support Optional Workload templates.

• Add design doc for the Template Engine
• Intergrate with the Optional Workload MOCK Library to query API
• Add autoinstallation/autoupdate of OW templates in the Hive for .Net 5
• Switch from the mock library to the real one, when it published to nuget.org
• Extend Hive cache with additional information about OW template
• Perform autocleaning of cache (uninstall OW template)

Testing phase

We need to complete the Tests:

• for the integration with real Optional SDK Workloads installation.
• perf test for installation/uninstallation (invoke the API call on every run, invoke cache cleaning on every run). The perf test should take into account number of templates installed in a system.