Http consistency: OpenAPI skills

[SergeyMenshykh]

Motivation, Context, and Description

1. In some cases, OpenAPI documents imported as OpenAPI skills or ChatGPT plugins may be malformed or non-compliant. However, they can still be processed and imported, even with minor differences from OpenAPI specification. To enable the import of these documents, the OpenAPI functionality error handling has been relaxed. Instead of halting the entire operation, parsing errors in the OpenAPI documents are skipped and logged.
2. The HTTP stack for OpenAPI skills aligned with connectors by offering two options:
   • using the internal SK HTTP client using provided configuration during Kernel building.
   • accepting a custom/external HTTP client, giving hosting applications/client code the freedom to use their own instance.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
• The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄