in dev.tfvars, opensearch_version is missing from stac_server_inputs config, causing the latest opensearch version to be used on initial deployment

[philvarner]

stac_server_inputs has an optional field opensearch_version that is not defined in the the example dev.tfvars file. However, this should always be defined, otherwise, the OpenSearch cluster version will be set to the latest at the time of first deployment, and then then never updated to newer versions. I believe it was not included under the mistaken understanding that a default in filmdrop-aws-tf-modules would be used instead, but it is instead only set as undefined, resulting in the behavior mentioned.