switch to openai compatible endpoints

[vabarbosa]

Description

this PR updates the extension to use the OpenAI compatible endpoints of the Qiskit Code Assistant service. it replaces the calls to the custom endpoint to calls the OpenAI endpoints

Linked Issue(s)

Fixes #108

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

this has been tested by running the extension against a local Ollama deployment of the Qiskit Code Assistant as well the remote Qiskit Code Assistant service deployment

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules