customize export columns

[itsmicaio]

This PR adds possibility to customize columns.

how to use:

• create array of columns:

const exportColumns = [
  {
    name: 'coupon',
    key: 'code', // key of record param
    callback: (value: string) => `30#${value}`, // optional callback to transform data
  },
  {
    name: 'name',
    concat: { // concat a list of record params by param key
      keys: ['firstName', 'lastName'],
      separator: ' ',
    },
  },
  {
    name: 'products',
    concat: { // concat an array record param
      key: 'products',
      separator: ', ',
    },
  }
]

• add options to feature builder

const adminJsOptions = {
...
    features: [
      importExportFeature({
        export: {
          columns: exportColumns
        },
        import: {
          isVisible: false
        }
      })
    ],
...
}