Change use of DefaultAzureCredential to ManagedIdentityCredential for Azure Log Analytics (#2811)

## Why make this change?
- It resolves issue #2810 
`ManagedIdentityCredential` class only authenticates with Azure Managed
Identity which makes it a better fit to use in AzureLogAnalytics than
`DefaultAzureCredential`.

## What is this change?
We stop using the `DefaultAzureCredential` class and instead start using
the `ManagedIdentityCredential` class.
Important Note: As of this moment with this change, the Azure Log
Analytics feature can only authenticate against system-assigned
identities.

## How was this tested?
- [ ] Integration Tests
- [ ] Unit Tests
- [X] Manual Tests
This change cannot be directly tested in the pipeline so it was tested
by using a VM and ensuring the logs are correctly sent to Azure Log
Analytics table.
- See #2787 for more information on how this was set up.

## Sample Request(s)
<img width="1028" height="448" alt="image"
src="https://github.com/user-attachments/assets/67221e39-4114-4fc2-ba72-1df3ed120b16"
/>

Author: RubenCerna2079

src/Service/Startup.cs

@@ -185,7 +185,7 @@ public void ConfigureServices(IServiceCollection services)
                 services.AddSingleton(sp =>
                 {
                     AzureLogAnalyticsOptions options = runtimeConfig.Runtime.Telemetry.AzureLogAnalytics;
-                    DefaultAzureCredential credential = new();
+                    ManagedIdentityCredential credential = new();
                     LogsIngestionClient logsIngestionClient = new(new Uri(options.Auth!.DceEndpoint!), credential);
                     return new AzureLogAnalyticsFlusherService(options, CustomLogCollector, logsIngestionClient, _logger);
                 });