Add reload and/or restart functionality to Chains

Feature request

in case of a config change or a change in external factors, users wish to be able to tell chains to reload the configuration OR restart the pod to read latest changes

Use case

our users have reported 2 use cases for this:

• MONGO_SERVER_URL has the creds to connect to mongo db which are rotated at a given cadence; when these creds are rotated, they wish to restart chains by hitting an endpoint (say /restart) so the pod restarts and the new creds are picked up
• there are times when updating chains-config configmap or signing-secrets secret does not result in configuration being picked up immediately by the chains controller pod - this is also evident in the getting start tutorial that says Then restart the controller to ensure it picks up the changes: - hitting a /reload (instead of /restart) will help such cases

Start with the getting-started tutorial linked in the issue and compare its restart guidance with the requested /reload and /restart behavior. Define how configuration changes and rotated MongoDB credentials should be picked up, then verify that the selected behavior is documented and testable for the Chains controller pod.