refactor(snap): Update command and metadata sourcing

[MonicaisHer]

• Inline CLIs flags
• Remove unused packages
• Remove external metadata sourcing

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/edgex-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

Build snap from this PR:

snap install --channel stable --classic snapcraft
snapcraft --use-lxd
# Snapped edgex-device-onvif-camera_3.0.0-dev.20_amd64.snap

Start the device:

sudo snap install --dangerous ./edgex-device-onvif-camera_3.0.0-dev.20_amd64.snap
sudo snap install edgexfoundry --channel=latest/edge
sudo snap connect edgexfoundry:edgex-secretstore-token edgex-device-onvif-camera:edgex-secretstore-token
sudo snap start --enable edgex-device-onvif-camera.device-onvif-camera

Check metadata:

$ snap info edgex-device-onvif-camera
name:      edgex-device-onvif-camera
summary:   EdgeX ONVIF Camera Device Service
publisher: –
store-url: https://snapcraft.io/edgex-device-onvif-camera
license:   Apache-2.0
description: |
  Refer to https://snapcraft.io/edgex-device-onvif-camera
services:
  edgex-device-onvif-camera.device-onvif-camera: simple, enabled, active
refresh-date: today at 11:10 CET
channels:
  latest/stable:    2.3.0        2022-11-11 (234) 12MB -
  latest/candidate: ↑                                  
  latest/beta:      ↑                                  
  latest/edge:      3.0.0-dev.21 2023-03-17 (465) 12MB -
installed:          3.0.0-dev.20             (x2) 12MB -

New Dependency Instructions (If applicable)

[presatish]

@MonicaisHer Can you please add the testing instructions above?

[MonicaisHer]

@presatish I have included the test instructions above. Here is also a GitHub Action for automatically testing Snap-related functions.