support for maintaining topic->storage pipe after upgrade

[turadg]

What is the Problem Being Solved?

Some durable objects links their topic/subscribers to storage. E.g. using forEachPublicationRecord

The watcher currently dies in upgrade and nothing resumes it.

Description of the Design

Use watchPromise.

Function signature approx,

  /**
   *
   * @template {object} T
   * @template {any[]} A args
   * @param {Promise<T>} p
   * @param {{onFulfilled: (T, ...A) => void, onRejected: (reason: any, ...A) => void}} watcher durable object handling resolution of the promise
   * @param {A} args added to calls to the watcher's handlers
   */
  function watchPromise(p, watcher, ...args) {

Assigning to @michaelfig because it fits into his overall Notifier revamp

Security Considerations

Scaling Considerations

Test Plan