biganimal_region resources should be renamed as biganimal_regions

[serdardalgic]

Although it's returning a List, the name of the data-source is singular.

That's against our Naming Conventions.

Changing this would be a breaking change. Please refer to Provider Data Source or Resource Rename Documentation for further details. Quoting there:

When renaming a resource from one name to another, it is important to keep backwards compatibility with both existing Terraform configurations and the Terraform state while operators migrate. To accomplish this, there will be some duplicated logic to support both resources until the next MAJOR release. Once both resources are appropriately handled, the process for deprecating and removing the old resource is the same as noted in the Provider Data Source or Resource Removal section.

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As of 21st of April, 2023; some more thinking on this ticket:

A possible solution would be

• creating a new data source called biganimal_regions
• marking biganimal_region as will be deprecated in the next major bump, please use biganimal_regions data source instead
• In the next major bump, we deprecate biganimal_region