Feat: Better mechanism for attaching middleware

[tofarr]

Better mechanism for configuring middleware

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below

---

Different environments will need different middleware. This PR moves the code for attaching middleware into the OpenhandsConfig so that it may be configured in an environment specific manner. This will also allow us to move SAAS specific middleware out of the OSS repo keeping the code cleaner and simpler.

---

Link of any specific issues this addresses

---

To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:bd21768-nikolaik   --name openhands-app-bd21768   docker.all-hands.dev/all-hands-ai/openhands:bd21768

[enyst]

We might want to restore the __version__ and other cool stuff you added the other day. 😅

Nice clean-up! We got away without one get_impl too. (just in time, we might add some get_impl in the runtime 😂, it is useful!)