Add transformation of SQL DB read error so HandleNotFound works

[rileykarson]

Cross-upstream of hashicorp/terraform-provider-google#6154

Release Note Template for Downstream PRs (will be copied)

sql: fixed behaviour in `google_sql_database` when the parent instance is deleted, removing it from state

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 27 insertions(+), 1 deletion(-))
Terraform Beta: Diff ( 2 files changed, 27 insertions(+), 1 deletion(-))