feat(changelog): make remote data available in context

[orhun]

Description

This PR updates the changelog processing order to make remote data (e.g. GitHub commits, pull requests, etc.) available in the context.

Motivation and Context

git cliff --github-repo orhun/git-cliff -c examples/github.toml -x --no-exec -u

This command will now contain the GitHub data such as:

 "github": {
      "contributors": [
        {
          "username": "bukowa",
          "pr_title": "style(lint): fix formatting",
          "pr_number": 702,
          "pr_labels": [],
          "is_first_time": true
        },
    ],
}

Might fix #687

How Has This Been Tested?

Locally.

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

Attention: Patch coverage is 83.78378% with 6 lines in your changes missing coverage. Please review.

Project coverage is 37.15%. Comparing base (b7e323f) to head (5368988).

Files	Patch %	Lines
git-cliff-core/src/changelog.rs	83.79%	6 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #703      +/-   ##
==========================================
+ Coverage   36.89%   37.15%   +0.27%     
==========================================
  Files          18       18              
  Lines        1350     1354       +4     
==========================================
+ Hits          498      503       +5     
+ Misses        852      851       -1     

Flag	Coverage Δ
unit-tests	37.15% <83.79%> (+0.27%)	⬆️

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