Plugin refactor

[TaoChenOSU]

Motivation and Context

Currently, plugin development using Chat Copilot has the following drawbacks:

1. CC requires the end user to configure the plugins and once configured, the plugins are transient, meaning that they disappear when the user refreshes the app.
2. Plugins are scoped to the user who configured them, meaning that all users who want to use plugins must independently configure them.

Description

This PR addresses the above issues by:

1. Move plugin configuration to the backend. Plugins are configured and added in the backend.
2. Save the states of plugins within chat sessions.
3. Create a new plugin call WebSearcher that performs Bing search. This plugin can be deployed to Azure.
4. Move the Klarna plugin to the backend.

This is not a breaking change.

This will be the first of a couple more PRs to come. The follow-up PRs will move the existing plugins that are still managed by the frontend to this new pattern.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the 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 😄

[dehoward]

@TaoChenOSU 61 files changed can be a lot to take in at once, is there any chance this PR can be broken up into 1 or more smaller PRs?

[TaoChenOSU]

@TaoChenOSU 61 files changed can be a lot to take in at once, is there any chance this PR can be broken up into 1 or more smaller PRs?

Yes, I will break this into multiple PRs.