fix(snap): Refactor to avoid conflicts with readonly config provider directory

[MonicaisHer]

Changes to incorporate the following fixes:

• Move env file to parent directory to avoid conflict with config provider canonical/edgex-snap-hooks#83
• Add snapctl wrapper to check connected interfaces canonical/edgex-snap-hooks#82

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/app-rfid-llrp-inventory/blob/main/.github/Contributing.md

PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?)
• I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• I have opened a PR for the related docs change (if not, why?)

Testing Instructions

Setup:

snap install ./edgex-app-rfid-llrp-inventory_3.0.0-dev.15_amd64.snap --dangerous
snap install ./edgex-config-provider/edgex-config-provider-example_2.3_amd64.snap --dangerous
snap install edgexfoundry --edge
sudo snap connect edgexfoundry:edgex-secretstore-token edgex-app-rfid-llrp-inventory:edgex-secretstore-token
sudo snap connect edgex-app-rfid-llrp-inventory:app-rfid-llrp-inventory-config edgex-config-provider-example:app-rfid-llrp-inventory-config

Validate that there are config files come from config provider:

$ snap start edgex-app-rfid-llrp-inventory && journalctl -f | grep "app=app-rfid-llrp-inventory source=service.go"
...app=app-rfid-llrp-inventory source=service.go:211 msg="CONFIG BY EXAMPLE PROVIDER"

Validate that .env file exists and works:

$ snap set edgex-app-rfid-llrp-inventory config.writable-loglevel=DEBUG
$ cat /var/snap/edgex-app-rfid-llrp-inventory/current/config/app-rfid-llrp-inventory/overrides.env 
# Sys-gen env vars from snap options:
WRITABLE_LOGLEVEL="DEBUG"

$ snap restart edgex-app-rfid-llrp-inventory && journalctl -f | grep app-rfid-llrp-inventory | grep DEBUG
# ... level=DEBUG ...

New Dependency Instructions (If applicable)