feat: add support for custom code push client headers, add x-cli-version header to CLI requests

[bryanoltman]

Description

• Adds support for additional headers in code push client requests
• Adds the x-cli-version to all code push client request headers made by the CLI

Part of #1910

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3dc991c) to head (2dc1e6d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #1913      +/-   ##
===========================================
+ Coverage   99.98%   100.00%   +0.01%     
===========================================
  Files         174       174              
  Lines        5476      5496      +20     
===========================================
+ Hits         5475      5496      +21     
+ Misses          1         0       -1     

Flag	Coverage Δ
shorebird_cli	100.00% <100.00%> (+0.02%)	⬆️
shorebird_code_push_client	100.00% <100.00%> (ø)

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