Add --disable-private-check runner option (#9556)

I forgot to add the `--disable-private-check` cmdline option in #8202. This PR fixes this:
```
> enso -h | grep -A2 private
--disable-private-check                Disables private module
checking at runtime. Useful for
tests.

```

engine/runner/src/main/scala/org/enso/runner/Main.scala

@@ -400,6 +400,11 @@ object Main {
       )
       .build()
 
+    val disablePrivateCheckOption = CliOption.builder
+      .longOpt(DISABLE_PRIVATE_CHECK_OPTION)
+      .desc("Disables private module checking at runtime. Useful for tests.")
+      .build()
+
     val options = new Options
     options
       .addOption(help)
@@ -445,6 +450,7 @@ object Main {
       .addOption(skipGraalVMUpdater)
       .addOption(executionEnvironmentOption)
       .addOption(warningsLimitOption)
+      .addOption(disablePrivateCheckOption)
 
     options
   }