Refactor variable declarations in Program.cs

Updated the declarations for `builder` and `app` to use explicit types (`WebApplicationBuilder` and `WebApplication`, respectively) instead of `var`. This change improves code clarity and readability.

Author: richard-einfinity

samples/datasync-server-cosmosdb-singlecontainer/src/Program.cs

@@ -12,7 +12,7 @@
 using System.Text.Json;
 using System.Text.Json.Serialization;
 
-var builder = WebApplication.CreateBuilder(args);
+WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
 
 string connectionString = builder.Configuration.GetConnectionString("DefaultConnection")
     ?? throw new ApplicationException("DefaultConnection is not set");
@@ -51,7 +51,7 @@
     .AddEndpointsApiExplorer()
     .AddSwaggerGen(options => options.AddDatasyncControllers());
 
-var app = builder.Build();
+WebApplication app = builder.Build();
 
 // Configure the HTTP request pipeline.
 if (app.Environment.IsDevelopment())