refactor: initialize config structs with default values

[Cyclonit]

Description

This change uses the embedded configuration to initialize configuration options with default values whenever possible. This moves the concern of defining default values into the embedded config and reduces complexity when using the configuration.

Motivation and Context

Closes #1087.

Using the embedded config.toml to initialize the config structs allows us to use well defined defaults in the code where previously we had to repeatedly unwrap Option<> in lots of places. The embedded config.toml was chosen because it is the config used by git-cliff itself and should follow all of our best practices.

This change also allowed for minimizing the fixtures' config files. Only values that are different to the defaults remain. Thus fixtures are less cluttered and easier to maintain.

How Has This Been Tested?

Regression testing was done using the existing fixtures and integration tests.

Screenshots / Logs (if applicable)

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have formatted the code with rustfmt.
• I checked the lints with clippy.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 44.18605% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.58%. Comparing base (cdce20f) to head (e61a31f).
⚠️ Report is 197 commits behind head on main.

Files with missing lines	Patch %	Lines
git-cliff/src/lib.rs	0.00%	19 Missing ⚠️
git-cliff-core/src/config.rs	50.00%	4 Missing ⚠️
git-cliff-core/src/changelog.rs	83.34%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1090      +/-   ##
==========================================
+ Coverage   41.27%   41.58%   +0.32%     
==========================================
  Files          21       21              
  Lines        1820     1816       -4     
==========================================
+ Hits          751      755       +4     
+ Misses       1069     1061       -8     

Flag	Coverage Δ
unit-tests	41.58% <44.19%> (+0.32%)	⬆️

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[orhun]

Nice! The config loading is pretty convenient, I added a comment about that.

[orhun]

Uh-oh, fixtures seems to be broken 😵

[orhun]

Just to double check: the fixture configs has been trimmed because we now have those values in the default config, right?

[Cyclonit]

Just to double check: the fixture configs has been trimmed because we now have those values in the default config, right?

Yes exactly. Imho duplicating default values over and over again is bad practice because it makes it difficult to find differences.

[orhun]

Awesome, thanks!