Simplify logic for master auth networks

[bharathkkb]

Currently we use a datasource to get the master auth network ranges, we should simplify that by exposing a set of variables that is set at each env root following the pattern here https://github.com/GoogleCloudPlatform/terraform-example-foundation-app/blob/b188297ad0c63b1e2228a33e5897ed8bfadc4d87/5-infrastructure/business_unit_1/development/main.tf#L30-L32

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