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

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

[github-actions[bot]]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[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 :warning:

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/dbt-labs/dbt-common/pull/192/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/dbt-labs/dbt-common/pull/192/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | `67.33% <66.66%> (+2.17%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs#carryforward-flags-in-the-pull-request-comment) to find out more.

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