feat: Add support for load/listen custom configuration

[lenny-goodell]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/go-mod-bootstrap/blob/master/.github/Contributing.md.

What is the current behavior?

No capability to load/listen for custom configuration

Issue Number: #179

What is the new behavior?

Now have capability to load/listen for custom configuration

Does this PR introduce a breaking change?

• Yes
• No

New Imports

• Yes
• No

Specific Instructions

Are there any specific instructions or things that should be known prior to reviewing?

Other information

[codecov-io]

Codecov Report

Merging #180 (7c2718f) into master (ecde49d) will decrease coverage by 5.90%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #180      +/-   ##
==========================================
- Coverage   54.30%   48.40%   -5.91%     
==========================================
  Files          14       14              
  Lines         615      690      +75     
==========================================
  Hits          334      334              
- Misses        270      345      +75     
  Partials       11       11              

Impacted Files	Coverage Δ
bootstrap/config/config.go	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ecde49d...7c2718f. Read the comment docs.