Consider merging more than 2 configurations

[dmtrKovalenko]

Hey, thanks for cool utility!
Oftentimes it's required to preserve the order of babel plugins. But curretly this lib is supporting only 2 configs to merge them. So I came up with the following:

const merge = require('babel-merge')
const rootConfig = require('../../babel.config')

const injectFirst = merge({ 
  plugins: ['idx']
}, rootConfig)

module.exports = merge(injectFirst, {
  presets: ['@emotion/babel-preset-css-prop'],
})

It will be much declarative if will be possible to do

module.exports = merge({ 
  plugins: ['idx']
}, rootConfig, {
  presets: ['@emotion/babel-preset-css-prop'],
})

I can open a PR for that