[CDTOOL-1233] ensure proper optional bool behavior in request_setting

[philippschulte]

Change summary

This PR resolves an issue related to the force_miss, force_ssl, bypass_busy_wait, and timer_support optional boolean fields in the request_setting block.

In Terraform, schema.TypeBool with Optional: true cannot distinguish between an unset value and one explicitly set to false. As a result, during updates involving unrelated field changes (e.g., default_host), these optional booleans could be omitted from the Fastly API update request — leading to unintended resets or configuration drift.

To prevent this, these optional booleans are now always included in the update payload, regardless of whether they’ve changed.

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Testing

• Added new acceptance test for preserving optional bool values:

=== RUN TestAccFastlyServiceVCLRequestSetting_PreserveBooleansDuringUpdate
=== PAUSE TestAccFastlyServiceVCLRequestSetting_PreserveBooleansDuringUpdate
=== CONT TestAccFastlyServiceVCLRequestSetting_PreserveBooleansDuringUpdate
--- PASS: TestAccFastlyServiceVCLRequestSetting_PreserveBooleansDuringUpdate (31.03s)

• Verified that existing acceptance tests for request_setting continue to pass:

=== RUN TestAccFastlyServiceVCLRequestSetting_basic
=== PAUSE TestAccFastlyServiceVCLRequestSetting_basic
=== CONT TestAccFastlyServiceVCLRequestSetting_basic
--- PASS: TestAccFastlyServiceVCLRequestSetting_basic (54.55s)

[rcaril]

LGTM!