`template_flow` method should be outside the client

[Sandro-Meireles]

Ideally, the FlowsRESTClient class should have a clear responsibility: contain flow clients

The template_flow method appears to be out of place among the clients. Furthermore, the name is not very suggestive either
https://github.com/weni-ai/weni-engine/blob/main/connect/api/v1/internal/flows/flows_rest_client.py#L341