feat(nextjs): Add instrumentation utility for server actions

[lforst]

Adds a withServerActionInstrumentation function that allows for wrapping the contents of server actions with Sentry instrumentation:

import * as Sentry from "@sentry/nextjs";
import { headers } from 'next/headers';

export default function ServerComponent() {
  async function myServerAction(formData: FormData) {
    "use server";
    return await Sentry.withServerActionInstrumentation(
      "myServerAction",
      { formData, headers: headers(), recordResponse: true },
      async () => {
        await fetch("http://example.com/");
        return { city: "Vienna" };
      }
    );
  }

  return (
    <form action={myServerAction}>
      <input
        type="text"
        defaultValue={"some-default-value"}
        name="some-text-value"
      />
      <button type="submit">Run Action</button>
    </form>
  );
}

Will look like:

I would have wanted the API to be the following but Next.js build time magic didn't allow it for some reason...:

import * as Sentry from "@sentry/nextjs";

export default function ServerComponent() {
  // ...
  return (
    <form action={Sentry.wrapServerAction('myServerAction', myServerAction)}>
      <input
        type="text"
        defaultValue={"some-default-value"}
        name="some-text-value"
      />
      <button type="submit">Run Action</button>
    </form>
  );
}

Fixes #9458