Provide the suggested way how to securely setup provider in the documentation.

[volodymyrZotov]

Currently, in the documentation we provide either this example to set up provider

// README.md
provider "onepassword" {
  url = "http://localhost:8080"
}

or this

// README in Terraform Registry (`templates/index.md.tmpl` file)
provider "onepassword" {
  URL                                 = "http://localhost:8080"
  token                               = "CONNECT_TOKEN"
  service_account_token = "SERVICE_ACCOUNT_TOKEN"
  op_cli_path                     = "OP_CLI_PATH"
}

Setting the sensitive values (tokens) directly in the terraform script is not secure, as it can be accidentally pushed and potentially leak the secrets. Therefore, the suggested and more secure way to set up the provider will be to use env variables OP_SERVICE_ACCOUNT_TOKEN to use service accounts and OP_CONNECT_TOKEN to use Connect.

We need to update the documentation to reflect this.