Set the root dir used for the object server including the metadata dir

[radu-tutueanu]

According to https://github.com/realm/realm-object-store/issues/263#issuecomment-263949456
We need support for setting the root dir used by OS
We currently have a workaround for the ROS to have the server running without being able to set the path.

@alazier

[sellmeadog]

I apologize if this is not the correct place to start this discussion, but I found myself here after researching how to change the location of the realm-object-server directory in Node.

I am struggling to understand what was actually changed in this PR to support specifying a custom sync directory and if it is still valid. I am trying to synchronize a Realm Cloud instance using Azure Functions and the presence of realm-object-server within the site root is problematic as whenever the directory is written to, it triggers a restart of the Azure Functions runtime.

My directory structure looks like this:

\site\realm
  \my.realm.management
  my.realm
  my.realm.lock
  my.realm.note
\site\wwwroot
  \function1
  \functionN
  \realm-object-server  

I need the ability to locate realm-object-server under \site\realm as this will prevent the Azure Function runtime from seeing changes to the file system triggering a runtime restart.

The only directory/path I seem to have any control over is the Realm file path. I have tried setting Realm.defaultPath and the path option in the Realm configuration to ...\realm\my.realm which resulted in the directory structure outlined above, i.e., no effect on the location of realm-object-server.

Please advise.