azurerm_automation_software_update_configuration: add default definition in software update

[wuxu92]

resolves: #21180 .

the document has mark this field Defaults to 'Etc/UTC' already.

--- PASS: TestAccSoftwareUpdateConfiguration_defaultTimeZone (297.21s)
PASS

[stephybun]

Thanks for this PR @wuxu92.

I checked the docs and it says the default is UTC but it should be updated to reflect the actual default value which is now Etc/UTC.

Also did this use to work/did the API change the default value from UTC to Etc/UTC? Could this change break users that have provisioned this resource using an older API version?

[wuxu92]

@stephybun sorry i forgot to update the document. and i find that the automation_schedule resource's timezone in document also not updated. so i updated this PR to fix the document too.

change information from release log as below. the software_udpate_configuration resource was introduced after v3.24, so i believe this PR should not cause any breaking change.

terraform-provider-azurerm/website/docs/guides/3.0-upgrade-guide.html.markdown

Line 393 in a931947

The default value for the field `timezone` will be changed from `UTC` to `Etc/UTC`.

[stephybun]

Thanks @wuxu92 LGTM 🌺

[github-actions]

This functionality has been released in v3.51.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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