Miscellaneous updates based on feedback

[cormacpayne]

This PR resolves the following items:

• Location : Canada Central #17
  • Introduces the location argument to specify the region that the Container App will be deployed to
  • Added documentation for this argument to call out how to find valid locations
• Does AzureContainerAppsRC task support sending Environment Variables along with build Image? container-apps-deploy-pipelines-task#4
  • Introduces the environmentVariables argument to specify a list of environment variables to set on the deployed Container App
• Cannot run AzureContainerAppsV0 tasks on Win32 agents container-apps-deploy-pipelines-task#6
  • Handles the OS of the runner that is executing the GitHub Action to account for how the pack CLI is installed
• Why task is downloading aditional code? container-apps-deploy-pipelines-task#3
  • Improves documentation to call out how the pack CLI is being installed by the action

[pauld-msft]