Infinitely Chainable Middleware Function on createServerFn

[ryant26]

Overview
The existing ergonomics of createServerFn do not allow for abstractions to be written and still retain the ability to mutate the object downstream. The alternative (global middleware) can be too heavy handed. This request is a proposal to allow the middleware() function to be called as many times as needed and to continuously append to the middleware array.

Example
It's not hard to imagine a scenario where a dev wants to create some light abstraction over the createServerFn function specific to their application:

// ServerFunctionUtils.ts
export const authenticatedMutationFn = createServerFn({
    method: "POST",
}).middleware([authMiddleware])

// AdministratorService.ts
export const updateOrganizationNameFn = authenticatedMutationFn().middleware([orgAdminMiddleware]).handler(() => {...})

Today you cannot call middleware() for a second time in the AdminstratorService file which limits your ability to create abstractions like this. The existing builder-like pattern of createServerFn seems like it would naturally allow for this.

Happy to contribute a PR if this seems like a good direction.