azurerm_automation_software_update_configuration - Refactor and add correct API constraints.

[jackofallops]

Adds schema validation and restrictions based on API limits / requirements:

• operating_system has been deprecated and is now controlled by the presence of either a linux or windows block.
• One of linux or windows block must now be present. This is a requirement of the API, so is a non-breaking Optional to Required change.
• monthly_occurrence - blocks limited to 1 due to:

Failure responding to request: StatusCode=400 -- Original Error:
        autorest/azure: Service returned an error. Status=400 Code="BadRequest"
        Message="{\"Message\":\"The request is
        invalid.\",\"ModelState\":{\"softwareUpdateConfiguration.properties.scheduleInfo.advancedSchedule.monthlyOccurrences\":[\"More
        than one Monthly Occurrence is not supported\"]}}"

• duration now defaults to PT2H as per the service.
• schedule block is now limited to 1, to match the API limit.
• schedule block is now Required to match the API specification. The API rejects requests that do not specify this block, with at least a frequency value.
• frequency is now a Required property of the schedule block. This is to match the minimum requirements of the API.
• pre_task blocks are now limited to 1 to match the API
• post_task blocks are now limited to 1 to match the API

closes #21970

[katbyte]

LGTM aside from one comment ☁️

[wuxu92]

Use a random location will cause test failure, because the required log analytics workspace location is not the same as the automation account's location in EastUS and EastUS2.

Error as below;

Original Error: autorest/azure: Service returned an error. Status=400 Code="BadRequest" Message="Error - chosen Azure Automation does not have a Log Analytics workspace linked for operation to succeed. To know which regions are supported for linking, see our documentation at: https://aka.ms/Automation-Region-Mapping