chatbot-rag-app: re-introduce ES cloud configuration

[codefromthecrypt]

When we refactored chatbot-rag-app, we started with local ENV. That said, many folks use ES cloud. We should add support in code and env.example for ES cloud connections, including opentelemetry setup.

Ideally, this can use canonical ENV variables used in other elastic tools, without us having to hard code if statements about cloud vs not. That said, I'm not sure if elasticsearch-py supports that at the moment.

[xeraa]

Why does this have to be Cloud specific? Won't the ELASTICSEARCH_URL (or whatever you're using) work locally as well as in any other environment?

[codefromthecrypt]

@xeraa Agree on the main app. This is more about the opentelemetry part, to make README or env.example comments of what to do when you are using Elastic cloud (for APM).

[codefromthecrypt]

Notes for when this is implemented cc @bshetti This comes after k8s in #396, and needs to do the following

Document and test Elastic Cloud for ES, but opentelemetry disabled

• Update env.example directions ELASTICSEARCH_URL such as we have for k8s, with an example cloud URL saying you also need to set ELASTICSEARCH_API_KEY
• Update README with a section about Elastic Cloud and make sure it is an anchor so we can reference it in the three ways to run: Docker, Python and Kubernetes
• Test default where OTEL_EXPORTER_OTLP_ENDPOINT is ignored due to default OTEL_SDK_DISABLED=true on Docker, Python and Kubernetes. So this means setting ELASTICSEARCH_URL and ELASTICSEARCH_API_KEY

Document and test Elastic Cloud for ES and OTEL

• Update env.example directions OTEL_EXPORTER_OTLP_ENDPOINT such as we have for k8s, with an example cloud URL and any authentication details that EDOT Pythonwill read.
• Update README opentelemetry section about elastic cloud, saying anything notable about how to get auth working
• Test OTEL_EXPORTER_OTLP_ENDPOINT when OTEL_SDK_DISABLED=false on Docker, Python and Kubernetes.

So, this is why I'm asking this to be solved in a separate PR as if this isn't done coherently someone will have to go back and clean it up later, or it would get lost in infrastructure for other changes. Hope it makes sense.

[codefromthecrypt]

k8s is merged, so if anyone wants this done elasticon week, it's on them as I am busy literally every day. if you do, many thanks!