feat: Add new ReadingClient API to service and context

[lenny-goodell]

closes #1476

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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?) Unit tests suffice
• I have opened a PR for the related docs change (if not, why?)
  feat: Document new ReadingClient APIs edgex-docs#1233

Testing Instructions

New Dependency Instructions (If applicable)

[vli11]

LGTM

[codecov-commenter]

Codecov Report

Merging #1482 (78362c1) into main (180f158) will increase coverage by 0.04%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1482      +/-   ##
==========================================
+ Coverage   66.89%   66.93%   +0.04%     
==========================================
  Files          35       35              
  Lines        3072     3076       +4     
==========================================
+ Hits         2055     2059       +4     
  Misses        881      881              
  Partials      136      136              

Files Changed	Coverage Δ
internal/app/service.go	59.61% <100.00%> (+0.22%)	⬆️
internal/appfunction/context.go	91.26% <100.00%> (+0.14%)	⬆️

[jim-wang-intel]

LGTM