Allow user petalinux to edit certain etc files via sudo

Add a sudo rule that allows user petalinux to edit the following files:

• /etc/network/interfaces (aka network config at site)
• /etc/powertools/* (aka power supply configuration)

The rule is added as part of the reception-setup package. Thus it will only be present in the sdcard configuration setup.

Note that in the sdcard configuration, /etc is mounted using overlayfs to allow for edits to be persistent.