Support preconfigured_waf_config field on rules for google_compute_security_policy resource

[modular-magician]

• fixes Support preconfigured_waf_config field on rules for google_compute_security_policy resource terraform-provider-google#12735

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Release Note Template for Downstream PRs (will be copied)

compute: added `preconfigured_waf_config` block to `google_compute_security_policy` resource (beta)

Derived from GoogleCloudPlatform/magic-modules#6730