Added Descope as OAuth Provider

[gaokevin1]

This PR adds Descope as a Default OAuth Provider with Convex, as is already the case with Auth0 and Clerk.

The PR that includes an example of a react app that uses this can be found here: get-convex/convex-demos#29

We have many customers who have asked us if we can work with Convex and are creating docs for them, but we would like to make it as easy as possible for our customers to use Descope with Convex. There are some concerns of using Convex from those who were already using Descope with another API Gateway because of this, but this should quell any of those concerns for our customers.

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[gaokevin1]

Is there a way I can include the guide on how to setup Descope as a Convex provider in the Docs, along with adding docs on the module created here, like this: https://docs.convex.dev/api/modules/react_clerk?