[Common Config Bootstrapper] Apply env overrides to values only when loaded from file

[lenny-goodell]

As decide in 3/15/2023 Architects meeting, Config Provider will be the System of Record for services' values.
This means that env overrides are only applied when configuration is loaded from file, including the common config file.
They are not applied to values loaded from Config Provider.
The overridden values are pushed into the Config Provider the first time the service starts or when the -o flag is used.

[farshidtz]

I believe the agreement was to remove the EdgeX v2 confusion that was being caused by pushing environment overrides to the config provider during startup. To my understanding, it was decided to apply environment variable overrides only when loading config from a file, that is when config provider is not used, and ignore them otherwise. This was documented in this issue originally as:

As decide in 3/15/2023 Architects meeting, Consul will be the System of Record for services' values.

This means that override are only applied when configuration is loaded from file, including the common config file.

However, the issue description and the implementation is now different and the EdgeX v2 issue persists. The user sets something during startup and it sticks. When unset, the override doesn't go away.

[cloudxxx8]

@farshidtz if we don't push the environment overrides to the Config Provider during the first time startup, the Config Provider would be seeded with the default config files only. For example, the other service client host will be localhost instead of core-metadata, which is the correct host name in the docker network environment. We leverage the environment variable overrides to adjust the config in the docker-compose files. It won't work in docker environment if we don't push the initial values.

[farshidtz]

The Common Config ADR is being modified to formalize the decisions: edgexfoundry/edgex-docs#1025