read and uses settings from the original index when settings argument is not given

[eunjae-lee]

If user doesn't pass settings argument, then we need to read the settings from Algolia server and apply them to the new temporary index. Otherwise, the settings will be lost.

https://github.com/algolia/gatsby-plugin-algolia/blob/master/gatsby-node.js#L167

Before this if statement, we could do something like

if (!settings && indexToUse === tempIndex) {
  settings = await index.getSettings()
}

If it's the same index, we don't need to get the whole settings and apply them again.

[Haroenv]

fix released in 0.9.0