Diff suppress storage transfer job start_time_of_day

[emilymye]

When start_time_of_day is not specified, the API returns start_time_of_day: {}, which Terraform then sets as "start_time_of_day" = map[string]string{ "hours": 0, "minutes": 0, ...}.

We want a diff suppress here so that:

• users can still supply empty value (no start_time_of_day or start_time_of_day = []) for modules or in general. Terraform will read the API default value in and the diff on second apply will be ignored.
• if the user changes it to an empty value, Terraform will only show a diff (and forcenew) if the previous value was not zero'd out. e.g. TF will ignore start_time_of_day.#: 1 => 0 but won't ignore .hours: 10 -> 0, and thus will still recreate it with an "empty" start time

Related to hashicorp/terraform-provider-google#3626

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[all]

[terraform]Diff suppress storage transfer job start_time_of_day

[terraform-beta]Diff suppress storage transfer job start_time_of_day

[ansible]

[inspec]

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
This PR seems not to have generated downstream PRs before, as of b9f8107.

Pull request statuses

No diff detected in terraform-google-conversion.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#723
depends: hashicorp/terraform-provider-google#3655

[rileykarson]

I'm a little hesitant to use a DSF for this purpose. I'm a little more supportive of not recording the field at all if the API returns an empty block (which we can tell by checking if any of the values are missing in the JSON, since they're all required), wdyt?

[emilymye]

Discussed offline - because we're using Golang clients, we need to do DSF since we can't tell difference between existing key with empty value and existing key with all-zero'd values