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

Also, removing the deprecated startup-duration and startup-interval options.

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/device-mqtt-go/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-device-mqtt_3.0.0-dev.14_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-device-mqtt:edgex-secretstore-token
sudo snap connect edgex-device-mqtt:device-mqtt-config edgex-config-provider-example:device-mqtt-config

Validate that there are config files come from config provider:

$ snap start edgex-device-mqtt && journalctl -f | grep "app=device-mqtt source=message.go"
level=INFO ts=2023-03-17T12:43:26.511670858Z app=device-mqtt source=message.go:55 msg="provided by config provider"

Validate that .env file exists and works:

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

$ snap restart edgex-device-mqtt && journalctl -f | grep device-mqtt | grep DEBUG
# ... level=DEBUG ...

New Dependency Instructions (If applicable)

[codecov-commenter]

Codecov Report

Merging #535 (1fb1655) into main (4e0b4e1) will not change coverage.
The diff coverage is n/a.

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  Lines         493      493           
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  Hits          106      106           
  Misses        373      373           
  Partials       14       14           

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