Upgrade guide - Add guidance for navigating region/location logic changes

[SarahFrench]

This guide accompanies this PR : #8587

Part of hashicorp/terraform-provider-google#14503

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 21 insertions(+))
Terraform Beta: Diff ( 1 file changed, 21 insertions(+))

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 21 insertions(+))
Terraform Beta: Diff ( 1 file changed, 21 insertions(+))