refactor: pass DbContextOptions into context directly

turns out efcore doesn't like it when we create a new options instance
(which includes a new data source *and* a new logger factory)
every single time we create a context. this commit extracts
OnConfiguring into static methods which are called when the context is
added to the service collection and when it's manually created for
migrations and the importer.

Foxnouns.Backend/Database/DatabaseServiceExtensions.cs

@@ -0,0 +1,21 @@
+using Serilog;
+
+namespace Foxnouns.Backend.Database;
+
+public static class DatabaseServiceExtensions
+{
+    public static IServiceCollection AddFoxnounsDatabase(
+        this IServiceCollection serviceCollection,
+        Config config
+    )
+    {
+        var dataSource = DatabaseContext.BuildDataSource(config);
+        var loggerFactory = new LoggerFactory().AddSerilog(dispose: false);
+
+        serviceCollection.AddDbContext<DatabaseContext>(options =>
+            DatabaseContext.BuildOptions(options, dataSource, loggerFactory)
+        );
+
+        return serviceCollection;
+    }
+}