feat(template): support using PR title in the GitHub template

[orhun]

Description

This PR makes it possible to use the pull request title with the GitHub integration:

* {{ commit.github.pr_title }}

The final context is the following:

"github": {
    "username": "orhun",
    "pr_title": "some things have changed",
    "pr_number": 420,
    "is_first_time": false
}

Motivation and Context

#148

How Has This Been Tested?

Locally / Fixture tests

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 (0ca4cdb) 42.42% compared to head (667b9a8) 42.53%.
Report is 3 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
+ Coverage   42.42%   42.53%   +0.12%     
==========================================
  Files          15       15              
  Lines         995      997       +2     
==========================================
+ Hits          422      424       +2     
  Misses        573      573              

Flag	Coverage Δ
unit-tests	42.53% <100.00%> (+0.12%)	⬆️

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