What is the problem you're trying to solve
Currently containerd uses supports text format for logs.

For example for /var/log/containers/coredns-*, the text log output would typically be in the format:
2020-01-10T18:10:40.01576219Z stdout F [INFO] plugin/reload: Running configuration MD5 = 4665410bf21c8b272fcfd562c482cb82

Describe the solution you'd like
I'd like the ability to configure containerd to write container logs using JSON format instead.

Re-using the example above of /var/log/containers/coredns-*, the JSON log format would be:
{"log":"[INFO] plugin/reload: Running configuration MD5 = 4665410bf21c8b272fcfd562c482cb82\n","stream":"stdout","time":"2020-01-10T17:22:50.838559221Z"}

Ideally, I'd like to use the configuration file at /etc/containerd/config.toml to switch between Text and JSON format for logs.

Additional context
This is for easy parsing by 3PP tools such as Elasticsearch and Splunk.