iotedge: default path to edged should be parsed from environment variable

[ef4203]

Description

For non-standard installations of Azure IoT Edge (e.g., where the path to 'edged' is in a different location), this hardcoded path of the 'edged' binary may or may not be present. This change enables package builders for non-standard installations to wrap the binary with the given environment variable. One example would be the Linux distribution NixOS, where all binaries are stored under /nix/store/.... Since this change doesn't affect standard installations (e.g., when the environment variable is not set, it defaults), the benefits outweigh the change.

Further information

I've already setup a pull request for this change (#7154), so this issue is just for reference.

[nyanzebra]

As PR #7154 is merged, closing this issue