docs: Add services configuration design doc

[derektriley]

Description:

Adds a markdown file explaining the purpose of the various *Config classes.

Related issue(s):

Fixes #16020

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +3.25% (target: -1.00%)	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (a0cc065)	99564	61377	61.65%
Head commit (ef6a159)	95496 (-4068)	61969 (+592)	64.89% (+3.25%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#16039)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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_{Codacy stopped sending the deprecated coverage status on June 5th, 2024. Learn more}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.38%. Comparing base (a0cc065) to head (ef6a159).
Report is 86 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #16039      +/-   ##
=============================================
+ Coverage      58.05%   61.38%   +3.33%     
- Complexity     19765    20099     +334     
=============================================
  Files           2726     2600     -126     
  Lines          99747    96679    -3068     
  Branches       10295    10044     -251     
=============================================
+ Hits           57908    59349    +1441     
+ Misses         38233    33732    -4501     
+ Partials        3606     3598       -8     

see 486 files with indirect coverage changes

[thomas-swirlds-labs]

LGTM! thanks @derektriley