[ ASE ] Allow for app settings to be configured through template variables

[erikschlegel]

All Submissions:

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• [YES] Have you followed the guidelines in our Contributing document?
• [YES] Have you added an explanation of what your changes do and why you'd like us to include them?
• [YES] I have updated the documentation accordingly.
• [NA] I have added tests to cover my changes.
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What is the current behavior?

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Currently, app service settings attributes are fixed properties controlled through the app service TF module.

Issue Number: #295

What is the new behavior?

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Technical operators are now able to configure App Setting key value pairs through the app_service_settings variable via the app service terraform module.

Does this introduce a breaking change?

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• [NO]

After using this configuration within the hello world template.

app_service_settings = {
  app_setting1 = "hw_setting_value",
  app_setting2 = "hw_setting_value"
}

Here's the settings from a deployed app service in azure portal