Python: Fix OpenAI/API plugins based on samples path changes. Black formatting for notebooks.

[moonbox3]

Motivation and Context

After kernel plugin revamp and restructing samples, the OpenAI/API plugin samples were not working.

Description

This PR fixes:

• The OpenAI/API plugin concept examples.
• Updates the 3rd getting_started notebook to match the behavior of dotnet where only chat completion is used, instead of text completion.
• Reformats via Black 2 getting_started notebooks.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python 3.10 Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel/connectors/openapi_plugin
openapi_manager.py	141	15	89%	15, 61–74, 104, 145, 150, 280, 350–363
TOTAL	5652	887	84%

Python 3.10 Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1280	1 💤	0 ❌	0 🔥	16.169s ⏱️

[moonbox3]

Was fixed in a subsequent PR. Closing.