[Resources.AWS] Replace IWebHost with IHost in tests

[martincostello]

Changes

Replace usage of IWebHost with IHost, which is marked as obsolete in .NET 10.

Cherry-picked from #2822.

Documentation: https://learn.microsoft.com/en-us/dotnet/core/compatibility/aspnet-core/10/webhostbuilder-deprecated

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.11%. Comparing base (2d3d158) to head (9ced990).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3096      +/-   ##
==========================================
+ Coverage   69.98%   70.11%   +0.13%     
==========================================
  Files         426      416      -10     
  Lines       16495    16444      -51     
==========================================
- Hits        11544    11530      -14     
+ Misses       4951     4914      -37     

Flag	Coverage Δ
unittests-Instrumentation.Cassandra	?
unittests-Resources.AWS	74.42% <ø> (ø)

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see 11 files with indirect coverage changes

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[Copilot]

Pull Request Overview

Updates the AWS ECS detector tests to replace the obsolete IWebHost with IHost for .NET 10 compatibility. This modernizes the test infrastructure while maintaining the same functionality.

• Replace IWebHost with IHost in the mock ECS metadata endpoint
• Update server configuration to use the new host builder pattern
• Simplify disposal methods with expression-bodied syntax

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