…nts (microsoft#7070)

### Motivation and Context

The Sessions Python Plugin was working properly, but some users reported
that the endpoints needed updating. We had made previous updates to the
plugin, but they didn't account for the update API endpoints and request
body changes shown
[here](https://learn.microsoft.com/en-us/azure/container-apps/sessions-code-interpreter).

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### Description

This PR updates the plugin tool to work with the documented endpoints
and request bodies. The unit tests were also updated. The concept sample
for the Azure Python sessions plugin was tested with all methods to:
execute code, upload multiple files, list files, and download them.
- Additionally, improve error handling for each of the function calls so
the proper error message is surfaced to the user via SK exceptions.
- Fix path building and making sure the sessions endpoint is converted
to a string from the Pydantic https type.
- Closes microsoft#6934 

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### Contribution Checklist

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- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄