Unit tests for the SensitiveDataLogger (#853)

## Motivation and Context (Why the change? What's the scenario?)

Contributing unit tests for the `SensitiveDataLogger` to cover a
recently fixed bug and prevent future regression.

## High level description (Approach, Design)

N/A - unit tests only

---------

Co-authored-by: Devis Lucato <[email protected]>

Author: alexmg

service/tests/Abstractions.UnitTests/Diagnostics/SensitiveDataLoggerTests.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.KernelMemory.Diagnostics;
+
+namespace Microsoft.KM.Abstractions.UnitTests.Diagnostics;
+
+public sealed class SensitiveDataLoggerTests : IDisposable
+{
+    private const string EnvironmentVariableName = "ASPNETCORE_ENVIRONMENT";
+
+    [Fact]
+    public void ItIsDisabledByDefault()
+    {
+        // Assert
+        Assert.False(SensitiveDataLogger.Enabled);
+    }
+
+    [Theory]
+    [Trait("Category", "UnitTest")]
+    [InlineData("development")]
+    [InlineData("Development")]
+    public void ItCanBeEnabledInDevelopmentEnvironment(string environment)
+    {
+        // Arrange
+        Assert.False(SensitiveDataLogger.Enabled);
+        Environment.SetEnvironmentVariable(EnvironmentVariableName, environment);
+
+        // Act
+        SensitiveDataLogger.Enabled = true;
+
+        // Assert
+        Assert.True(SensitiveDataLogger.Enabled);
+    }
+
+    [Theory]
+    [Trait("Category", "UnitTest")]
+    [InlineData("staging")]
+    [InlineData("Staging")]
+    [InlineData("production")]
+    [InlineData("Production")]
+    [InlineData("any")]
+    public void ItCannotBeEnabledInNonDevelopmentEnvironments(string environment)
+    {
+        // Arrange
+        Assert.False(SensitiveDataLogger.Enabled);
+        Environment.SetEnvironmentVariable(EnvironmentVariableName, environment);
+
+        // Act/Assert
+        Assert.Throws<InvalidOperationException>(() => SensitiveDataLogger.Enabled = true);
+    }
+
+    [Theory]
+    [Trait("Category", "UnitTest")]
+    [InlineData("development")]
+    [InlineData("Development")]
+    [InlineData("staging")]
+    [InlineData("Staging")]
+    [InlineData("production")]
+    [InlineData("Production")]
+    [InlineData("any")]
+    public void ItCanBeDisabledInAnyEnvironment(string environment)
+    {
+        // Arrange
+        Assert.False(SensitiveDataLogger.Enabled);
+        Environment.SetEnvironmentVariable(EnvironmentVariableName, environment);
+
+        // Act
+        SensitiveDataLogger.Enabled = false;
+
+        // Assert
+        Assert.False(SensitiveDataLogger.Enabled);
+    }
+
+    public void Dispose()
+    {
+        Environment.SetEnvironmentVariable(EnvironmentVariableName, null);
+        SensitiveDataLogger.Enabled = false;
+    }
+}