Print final configuration on startup

[dashpole]

Is your feature request related to a problem? Please describe.
This is related to the problem described in https://github.com/open-telemetry/opentelemetry-collector/issues/2163. The collector does environment variable substitution with the provided configuration. Prometheus receiver configurations often use $ as part of the configuration, which makes it easy to accidentally reference environment variables when you don't intend to.

Additionally, when using deployment systems such as kubernetes, environment variables themselves may be programmatically populated, making the final configuration used to run the collector difficult to determine.

Describe the solution you'd like
The collector should print out the final configuration used on startup after environment variables have been substituted.

Describe alternatives you've considered
Alternatively, we can do nothing.

[dashpole]

I realized this is actually a duplicate of #1791