What is the problem you're trying to solve

Today the config.toml houses all the runtime config.
When you need to add/change a runtime you have to restart containerd.
Also the config itself gets large and unwieldy.
Injecting a runtime into the main config can also be troublesome when trying to do so from an automated installer.

Describe the solution you'd like

Much in the same way cri registry configs were extracted, I propose we extract runtime config like to something like /etc/containerd/runtimes/<handler>/config.toml

Each time a config needs to be resolved it should load from this config file.
This allows adding/updating runtime handlers without restarting containerd.

Additional context

An example that may benefit from this is https://kwasm.sh