source_sftp: Remove file extension from stream name

[eugenekim-orrum]

Source SFTP v0.2.1

Stream names include the file extension, which in turn creates destination tables named with the file extension in the table name.
For example, if ingesting a file named test.csv, the stream name becomes "test.csv" and then in turn the destination table created is named "test.csv". In my case, Snowflake handles table names with periods but requires quoting and is just confusing in general.
The destination table name in my opinion should never include a file extension but I did some searches and so far nobody has complained about it yet so maybe I'm in the minority?