Add additional context cancellation location

While an improved ability to detect Ctrl+C context cancellation was added in #933 I was noticing in this branch that when using the `--show-details` output after pressing Ctrl+C I would still see a lot
of extra output displayed about data files being processed that were actually getting skipped so this helps to add an extra cancellation check to avoid that unneeded output.

internal/dumper/loader.go

@@ -107,6 +107,11 @@ func (l *Loader) Run(ctx context.Context) error {
 		numberOfDataFiles := len(files.tables)
 
 		for idx, table := range files.tables {
+			// Allows for quicker exit when using Ctrl+C at the Terminal:
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+
 			table := table
 			conn := pool.Get()