Add "object" mergebehavior to MergeBehavior processing

[gshank]

resolves #191

Description

Add a new type of MergeBehavior, "Object". Move the processing of config_call_dicts to the same file. Create tests for both types of merges.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[github-actions]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 16 lines in your changes missing coverage. Please review.

Project coverage is 67.33%. Comparing base (9798ca7) to head (72506cb).

Files with missing lines	Patch %	Lines
dbt_common/contracts/config/base.py	66.66%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #192      +/-   ##
==========================================
+ Coverage   65.16%   67.33%   +2.17%     
==========================================
  Files          52       52              
  Lines        3333     3380      +47     
==========================================
+ Hits         2172     2276     +104     
+ Misses       1161     1104      -57     

Flag	Coverage Δ
unit	67.33% <66.66%> (+2.17%)	⬆️

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