containerd
Configure otel from env instead of config.toml
These are standard environment variables described by the otel spec in https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/.
Config options are converted to OTEL envs, but setting from environment overrides the config.
Also since otel will by default try to connect to https://localhost:4318 if no endpoint is set, this will also just disable the otlp plugin when there is no endpoint so we don't have otel continuously trying to connect to the default endpoint, littering the logs with connection failure messages and collecting traces that won't go anywhere.
Closes #8801
PR needs rebase.
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I think this makes sense for 2.0. How would we want to backport support for this to 1.6/1.7? We would want to utilize the deprecation warnings there now too.
For the failure, update the 1.6 and 1.7 config to match the new default at https://github.com/containerd/containerd/tree/main/integration/client/testdata . I have been adding a comment and keeping the original value so we have documentation of changes to the default configurations from 1.6 and 1.7.
