Allow Server Action header token pinning

[ptvty]

Goals

1. Better developer experience while debugging complicated apps with calls to different server actions
2. Being able to test endpoints in isolation

Non-Goals

No response

Background

The Network tab in browsers' DevTools provide a convenient place to monitor and debug client-server interactions. In a legacy REST API, one can easily know which server function is being called by checking the URL.
After switching to Server Actions in a web application with lots of server actions being called from different client components its very difficult to distinguish which server action is being called as all you have is a random token sent as a request header (next-action ).
Also if you choose to test these endpoints in isolation from the calling client - as after all, Server Actions are public facing REST APIs listening for POST requests - there is no easy way to find the token assigned to each server action.

Proposal

const addAction = (a, b) => a + b

addAction.actionName = 'add-action'  // <-- use this string instead of generated token

export default addAction

Now we can:

• Check the request header and know which action is this in the Network tab.
• Send test requests targeted at specific action via network tools like Postman for testing / debugging purposes.