fix(shorebird_cli): don't prompt users for confirmation if we can't accept input via stdin

[bryanoltman]

Description

If running in a terminal-less environment, Shorebird should not prompt for user confirmation.

Fixes #1705

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 (0e14f8b) to head (636fc29).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1845   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          173       173           
  Lines         5478      5479    +1     
=========================================
+ Hits          5478      5479    +1     

Flag	Coverage Δ
shorebird_cli	100.00% <100.00%> (ø)

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[eseidel]

lgtm. We may still want to consider a "--no-confirm" or "--non-interactive" or whatever the pattern is.