Expose `RetryOptions` type

[denchen]

I'm requesting officially exposing the RetryOptions type from packages/toolkit/src/query/retry.ts. My use case is that I've created a wrapper around fetchBaseQuery() that includes retry options as well as some of my app-specific options, and so I've been importing RetryOptions from @reduxjs/toolkit/dist/query/retry even though it's not an official export.