Adding DiffSuppress for pd-ssd and pd-hdd

[modular-magician]

Potential fix for Issue #10492 google_sql_database_instance permanent diff when disk_type is set to pd-ssd
hashicorp/terraform-provider-google#10492

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Release Note Template for Downstream PRs (will be copied)

google_sql_database_instance: fixed a bug causing a perma-diff on disk_type due to API values being downcased

Derived from GoogleCloudPlatform/magic-modules#6537