[Infra] Remove redundant System.Text.Json / update to 8.0.5 where needed

[martincostello]

Changes

Remove references to System.Text.Json from target frameworks where it is already included in-box for the shared framework (.NET 8+).

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 74.95%. Comparing base (7c67fd4) to head (cba218f).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4154      +/-   ##
==========================================
- Coverage   74.99%   74.95%   -0.04%     
==========================================
  Files         467      467              
  Lines       18441    18429      -12     
==========================================
- Hits        13830    13814      -16     
- Misses       4611     4615       +4     

Flag	Coverage Δ
unittests-Exporter.InfluxDB	95.81% <ø> (ø)
unittests-Instrumentation.AWS	83.54% <ø> (ø)
unittests-Instrumentation.ElasticsearchClient	80.60% <ø> (ø)
unittests-Resources.AWS	74.49% <ø> (ø)
unittests-Resources.Azure	88.31% <100.00%> (ø)
unittests-Resources.Gcp	71.42% <ø> (ø)
unittests-Sampler.AWS	94.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...emetry.Resources.Azure/AzureVmMetaDataRequestor.cs	75.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[Copilot]

Pull request overview

This PR removes redundant System.Text.Json package references for TFMs where System.Text.Json is already provided by the shared framework (.NET 8+), while keeping conditional references for older TFMs that still need the NuGet package.

Changes:

• Removed unconditional System.Text.Json PackageReference entries from several projects.
• Added/converted conditional PackageReference Include="System.Text.Json" entries for TFMs < net8.0 (using IsTargetFrameworkCompatible or .NETStandard conditions).
• Adjusted Update-style overrides to Include where the unconditional reference was removed.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/OpenTelemetry.Sampler.AWS/OpenTelemetry.Sampler.AWS.csproj	Drops unconditional System.Text.Json; keeps it only for TFMs < net8.0 with VersionOverride.
src/OpenTelemetry.Resources.Gcp/OpenTelemetry.Resources.Gcp.csproj	Drops unconditional System.Text.Json; keeps it only for .NETStandard TFMs with VersionOverride.
src/OpenTelemetry.Resources.Azure/OpenTelemetry.Resources.Azure.csproj	Drops unconditional System.Text.Json; keeps it only for .NETStandard TFMs with VersionOverride.
src/OpenTelemetry.Resources.AWS/OpenTelemetry.Resources.AWS.csproj	Replaces identifier-based condition with < net8.0 compatibility check; keeps System.Text.Json only when needed.
src/OpenTelemetry.Instrumentation.ElasticsearchClient/OpenTelemetry.Instrumentation.ElasticsearchClient.csproj	Moves System.Text.Json reference into a conditional ItemGroup for TFMs < net8.0.
src/OpenTelemetry.Instrumentation.AWSLambda/OpenTelemetry.Instrumentation.AWSLambda.csproj	Drops unconditional System.Text.Json; keeps it only for TFMs < net8.0 with VersionOverride.
src/OpenTelemetry.Exporter.InfluxDB/OpenTelemetry.Exporter.InfluxDB.csproj	Makes System.Text.Json reference conditional for TFMs < net8.0 (removing it for net8+).

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