feat: use AppRun file name as prefix of the .env file path

[azubieta]

Goal: Allow defining a different runtime configuration for each binary in a bundle if required.

Features:

• .env file path is created using the AppRun file path as prefix. I.E.: '/AppDir/usr/bin/AppRun.env'
• A new self defined environment variable is introduced ORIGIN which points to the AppRun file.
• AppRun relative .env files must define the APPDIR variable relative to ORIGIN
• Fallback to the legacy implementation and is meant to be a drop in replacement.

Closes #27