Fix serverless authentication not working

[rblcoder]

Description

Authentication for serverless has stopped working

Issues Resolved

Issue #179

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[rblcoder]

@prudhvigodithi Have tested with both these provider configurations with AWS OpenSearch Serverless

provider "opensearch" {
  url = "url"
  healthcheck        = "false"
  aws_profile = "profilename"
  aws_assume_role_arn = "rolearn"
  aws_assume_role_external_id = "externalid"
  aws_region          = "region"
  version_ping_timeout = "10"

}

and

provider "opensearch" {
  url = "url"
  healthcheck        = "false"
  aws_region          = "region"
  aws_access_key = "access key"
  aws_secret_key = "secret"
  version_ping_timeout = "10"

}

[prudhvigodithi]

Had an offline discussion with @rblcoder and this code works, but however we should remove the osVersion info.Version.Number usages across the code as with branching and release of the terraform provider there is a compatibility matrix that will handle the right OpenSearch versions.
https://github.com/opensearch-project/terraform-provider-opensearch/blob/main/COMPATIBILITY.md
@bbarani