Add the migration path from 7.x-1.x

Changes from D7 to D8 :
Removed the admin configuraiton form to set the default values. Use the block configuration to set the save the values per block basis instead of default values.

So the question here is in D7 we have two variables which saves the default values.
google_currency_converter_from
google_currency_converter_to

What would the destination plugin ? Where we should save the d7 block settings in d8 ? will it be in config ?

Note : The patch is incomplete which only contains the migration template which only has the source plugin information, we need to add the process and destination, for this the question is above.