feat: third party app support in EVADB

[kaushikravichandran]

This PR introduces a generic interface to support 3rd party apps in EVADB. As an example. the template for integrating slack has been added. In a subsequent PR the integration with slack will be completed.

[jiashenC]

I'd like to understand the context of this PR better. We discussed the Slack chatbot use case yesterday, and I believe that it can be a standalone app without changing EvaDB internally or adding third-party integrations.

Is this PR going to facilitate some other new use cases? If so, could you give some detailed examples here and also explain a bit about how it will interact with EvaDB?

Thank you!

[jarulraj]

That's a big PR, @kaushikravichandran! Nice job, let's wrap it up.

[jarulraj]

If it is good to merge, let's do that. Students working on application integrations will require the handler inferface.

[xzdandy]

I will take care of the PR.

[kaushikravichandran]

I will take care of the PR.

Thanks. I have resolved the latest set of conflicts now.

[jarulraj]

@kaushikravichandran Please add docs for the app handler interface soon as students will need it.

[jarulraj]

Any reason the unfortunately repeated conflict merging on this PR. @xzdandy @kaushikravichandran

[jarulraj]

@kaushikravichandran is reducing the size of this PR.