feat: add openai inference provider (#46)

# What does this PR do?

New optional provider.

Relates to: RHAIENG-1198


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- New Features
  - Added support for OpenAI as a remote inference provider.
- Automatically enabled when OPENAI_API_KEY is set; supports
configurable base URL (default: https://api.openai.com/v1).

- Documentation
  - Updated provider list to include the OpenAI remote inference option.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: leseb

distribution/README.md

@@ -16,6 +16,7 @@ You can see an overview of the APIs and Providers the image ships with in the ta
 | inference | inline::sentence-transformers |
 | inference | remote::azure |
 | inference | remote::bedrock |
+| inference | remote::openai |
 | inference | remote::vertexai |
 | inference | remote::vllm |
 | inference | remote::watsonx |

distribution/build.yaml

@@ -9,6 +9,7 @@ distribution_spec:
     - provider_type: remote::watsonx
     - provider_type: remote::azure
     - provider_type: remote::vertexai
+    - provider_type: remote::openai
     vector_io:
     - provider_type: inline::milvus
     - provider_type: remote::milvus

distribution/run.yaml

@@ -54,6 +54,11 @@ providers:
     config:
       project: ${env.VERTEX_AI_PROJECT:=}
       location: ${env.VERTEX_AI_LOCATION:=us-central1}
+  - provider_id: ${env.OPENAI_API_KEY:+openai}
+    provider_type: remote::openai
+    config:
+      api_key: ${env.OPENAI_API_KEY:=}
+      base_url: ${env.OPENAI_BASE_URL:=https://api.openai.com/v1}
   vector_io:
   - provider_id: milvus
     provider_type: inline::milvus