feat: add vendorfield to list of exportable options

[arkmoon]

Made this change for myself, thought I could contribute if this is something anyone else needed.

Helps distinguish transactions that are listed, and allows you to sort by Smartbridge in case you have specific groupings you need to organize your transactions into.

Let me know if I need to make any additional changes @dated

[dated]

the stored options need to be merged with the default options, otherwise the vendorField toggle won't be visible, something like:

    exportOptions () {
      const defaultOptions = {
        delimiter: ',',
        includeHeaders: true,
        columns: {
          date: true,
          crypto: true,
          fiat: true,
          vendorField: true,
          id: true
        }
      }

      const storedOptions = walletApi.storage.get('exportOptions', true)

      if (!storedOptions) {
        return defaultOptions
      }

      const columns = {
        ...defaultOptions.columns,
        ...storedOptions.columns
      }

      return {
        ...defaultOptions,
        ...storedOptions,
        columns
      }
    },