Create "synchronize" as a common, installable, endpoint

[ryckmanat]

The example servers all add an "/synchronize" endpoint (which is, optionally, protected). It looks like this today:

    const synchronizeEndpoint = {
      method: ['POST', 'GET'],
      handle: async () => {
        await storageDriver.synchronize(true);
        return 'ok - db initialized';
      },
    } as CustomRequestHandler;

Given that this is commonly wanted, we should move it to the opr-core library and make it easily installable in any server.

This should be created under opr-core/src/server/installable-endpoints/synchronize.ts. Then, export the endpoint as a CustomRequestHandler.