feat(parser): support using regex scope values

[orhun]

Description

This PR makes it possible to use regex-replace for the scope value in commit_parsers:

[git]
# regex for parsing and grouping commits
commit_parsers = [
  { message = "^\\[(.*)\\]", group = "Changes to ${1}", scope = "${1}" },
]

In this example, [codebase]: rewrite everything in Rust will appear in the changelog as:

### Changes to codebase

- (codebase) Rewrite everything in Rust

Motivation and Context

closes #371

How Has This Been Tested?

test fixtures

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

All modified and coverable lines are covered by tests ✅

Comparison is base (991a035) 42.65% compared to head (268b71a) 42.73%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #372      +/-   ##
==========================================
+ Coverage   42.65%   42.73%   +0.09%     
==========================================
  Files          13       13              
  Lines         666      667       +1     
==========================================
+ Hits          284      285       +1     
  Misses        382      382              

Flag	Coverage Δ
unit-tests	42.73% <100.00%> (+0.09%)	⬆️

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