Made google_document_ai_processor_default_version test ignore changes to version field

[modular-magician]

Resolved #12905 by altering the test to ignore changes (and improving documentation.)

projectNumberDiffSuppress is already in place to handle diffs based solely on the project id -> project number change; the larger issue is that the API replaces release channels (now called "stable" and "rc") with specific API versions. Unfortunately, this API does not supply a way to extract the list of versions in a particular release channel, so there's no way to make a data source to get the "latest stable version" and have the resource use that. Fully suppressing the diff in the provider would mislead users into thinking that they are on the latest stable or rc release, when in fact they might be extremely out of date.

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Derived from GoogleCloudPlatform/magic-modules#7317