add folder_id to google_folder docs

[BBBmau]

Fixes hashicorp/terraform-provider-google#15914

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

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[modular-magician]

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Diff report

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

Terraform GA: Diff ( 1 file changed, 1 insertion(+))
Terraform Beta: Diff ( 2 files changed, 6 insertions(+))