Infer Azure region from endpoint

[jnu]

When the region is not set in the runtime config, it can be inferred from the openai service endpoints. This also solves the issue of having cross-region deployments.

[sentry]

Bug: The _azure_region function may incorrectly extract a region from an Azure OpenAI hostname if the name doesn't contain a hyphen, causing cost estimation to fail.
_{Severity: MEDIUM}

Suggested Fix

The _azure_region function should be updated to handle hostnames without a hyphen. One approach is to return None if rsplit("-", 1) results in a list with only one element, indicating no hyphen was found. Alternatively, the extracted value could be validated against a list of known Azure region names.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: bc2/core/common/openai.py#L634

Potential issue: The `_azure_region` function attempts to infer the Azure region by
splitting the resource hostname on the last hyphen. However, if an Azure OpenAI resource
name does not contain a hyphen (e.g., `myresource.openai.azure.com`), the function will
incorrectly return the entire resource name as the region. This invalid region name is
then used to query the Azure Retail Prices API, which returns no results. Consequently,
the application will raise an `AzurePricingUnavailable` exception, preventing cost
estimation for that resource.

_{Did we get this right? 👍 / 👎 to inform future reviews.}