[bug] embedding microservice almost openai compatible but not fully

[rbrugaro]

We claim OPENAI compatible but OPEA still returns some objects as null that should be populated.
OPEA TEI: "usage":null, "model":null,
Bare TEI: "model":"BAAI/bge-large-en-v1.5","usage":{"prompt_tokens":12,"total_tokens":12}

This issue of milling objects applies to other microservices too. Might be good to systematically correct for all.