Adjust tgw transit_gateway_cidr_blocks validation

[wedge-jarrad]

Transit gateway service quotas list 5 as the maximum CIDR blocks per transit gateway and it is not adjustable. https://docs.aws.amazon.com/vpc/latest/tgw/transit-gateway-quotas.html

API docs specify a minimum CIDR block of /24 or /64 for IPv4 and IPv6, respectively. It does not specify a maximum size. https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_TransitGatewayRequestOptions.html

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Closes #25316

Output from acceptance testing:

Tests not run because it seems that all of the little tests are tied together into one huge test.

[ewbankkit]

LGTM 🚀.

[ewbankkit]

@wedge-jarrad Thanks for the contribution 🎉 👏.

[github-actions]

This functionality has been released in v4.22.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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[github-actions]

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