Support nested objects in template_properties

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template_properties in the provider can only support key(string):value(string) pairs. The backing API can support key(string):value(any) pairs, like this:

{
    "someKey": {
        "nestedValue": ["thing", "thing", "thing"]
    },
    "someOtherKey": "value",
    "finallyKey": ["stuff"]
}

To support arbitrary key:value pairs we need to change template_properties from a Terraform Map to a String of JSON. Similar to how the aws_iam_policy resource does things: reference.

This is a breaking change so we're not going to make it lightly. If you have concerns about this change let us know. If necessary, we will support two workflows for a while with a deprecation period for the old map-based template_properties.

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To elaborate on the "supporting two workflows": We would probably add a new field, maybe called template_props which is the new "String of JSON" field. The old template_properties would then be marked as deprecated and removed in a later release.

Here's some info about how to deprecate attributes in a Terraform provider: reference