Is anyway to add sample data in the format of csv or excel files to the MetaBase ?
Currently no, but you can go and vote on this issue by clicking the on the first post:
Metabase really needs a bit more structured data to make any sense of it - in other words; it needs a database to do it’s queries.
I’m not sure if you can somehow add data to Google Spreadsheet and then use the database type BigData in Metabase to gain access to the sheet.
There’s an issue raised about getting access to a sheet directly: