Update PersistenceManager not to fail when used in a read-only file system

[dscpinheiro]

Fixes #3801

Description

Updates the SDK's PersistenceManager not to fail when running on a read-only file system.

I also included the suggested new option to ignore the legacy persistence store when the SDK is going through the default profile resolution search (via the CredentialProfileStoreChain).

Motivation and Context

#3801 and DOTNET-8123

Testing

• Dry-run: DRY_RUN-5960c79f-a0e7-4dad-97c9-61374e1d2324
• I also created a console app using the PersistenceManager class directly and confirmed running it in a read-only file system does not throw a terminating error anymore:

using Amazon;
using Amazon.Runtime.Internal.Settings;

AWSConfigs.LoggingConfig.LogTo = LoggingOptions.Console;
AWSConfigs.LoggingConfig.LogMetricsFormat = LogMetricsFormatOption.JSON;
AWSConfigs.LoggingConfig.LogResponses = ResponseLoggingOption.Always;
AWSConfigs.LoggingConfig.LogMetrics = true;

var instance = PersistenceManager.Instance;
Console.WriteLine($"Got here! Instance type is {instance.GetType()}");

Before:

PS> docker run --read-only --rm my-dotnet-app
Unhandled exception. System.TypeInitializationException: The type initializer for 'Amazon.Runtime.Internal.Settings.PersistenceManager' threw an exception.
 ---> System.IO.IOException: Read-only file system : '/root/AppData'

After:

PS> docker run --read-only --rm my-dotnet-app
PersistenceManager 1|2025-07-10T23:52:15.244Z|ERROR|Unable to initialize 'PersistenceManager'. Falling back to 'InMemoryPersistenceManager'. --> System.IO.IOException: Read-only file system : '/root/AppData'
Got here! Instance type is Amazon.Runtime.Internal.Settings.InMemoryPersistenceManager

Types of changes

• Bug fix (non-breaking change which fixes an issue)

License

• I confirm that this pull request can be released under the Apache 2 license