refactor(googleapis_auth): rename AuthProvider to AuthEndpoints

[bryanoltman]

Description

A future PR is going to introduce an AuthProvider enum. Because the googleapis_auth AuthProvider is just a pair of endpoints, call it AuthEndpoints to reduce confusion.

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 (67a06e7) to head (3a18fa0).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1755   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          165       165           
  Lines         5136      5136           
=========================================
  Hits          5136      5136           

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

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