fix: [Terraform] Store SHA 256 of certificate SSL private keys

[hyww]

related issue:

• Don't store SSL private_key in the tfstate file hashicorp/terraform-provider-google#6119
• Don't store SSL private_key in the tfstate file hashicorp/terraform-provider-google#927 (old one, closed)

custom_flatten introduced in #1336 doesn't work for privateKey field since it has ignore_read set to true. Use state_func instead.

see also: hashicorp/terraform-provider-google#2976

both the custom_flatten function and sha256DiffSuppress were removed because:

• there seems no other usage of those functions
• usage of Sum is not correct in those functions

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

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@emilymye, please review this PR or find an appropriate assignee.

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 4 files changed, 25 insertions(+), 20 deletions(-))
Terraform Beta: Diff ( 4 files changed, 25 insertions(+), 20 deletions(-))

[modular-magician]

Oops! It looks like you're using an unknown release-note type in your changelog entries:

• REPLACEME

Please only use the types listed in https://github.com/GoogleCloudPlatform/magic-modules/blob/master/.ci/RELEASE_NOTES_GUIDE.md.

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 4 files changed, 26 insertions(+), 20 deletions(-))
Terraform Beta: Diff ( 4 files changed, 26 insertions(+), 20 deletions(-))

[modular-magician]

Oops! It looks like you're using an unknown release-note type in your changelog entries:

• REPLACEME

Please only use the types listed in https://github.com/GoogleCloudPlatform/magic-modules/blob/master/.ci/RELEASE_NOTES_GUIDE.md.

[danawillow]

This PR looks good functionally, but it doesn't conform to the state-setting model that we'll eventually need to adhere to (more info in hashicorp/terraform-provider-google#4328). I've reached out to try to get more information on what we can do here.

[danawillow]

Ok, I've heard back from HashiCorp, and it's pretty much what I expected- future versions of the SDK won't allow having a value in the config but not in state. Because of this, I don't think it's worth temporarily fixing this use case when we won't be able to in the future. Sorry about this! I wish I had better news for you. Feel free to file an issue in https://github.com/hashicorp/terraform-plugin-sdk if you want to follow up with the people working on the SDK.

Closing this out.