Allow to specify client certificate path explicitly

[dongwoo1005]

As per discussion in Slack: https://prestosql.slack.com/archives/CFPVDCDHV/p1589924393017200

Currently presto.dbapi.connect api does not have a parameter to explicitly specify client certificate path to connect with SSL/TLS. Client cert should be explicitly configurable.

[findepi]

A current workaround, from referenced slack thread:

After creating the connection object I do

conn._http_session.verify = '/path/to/cert' 

before creating a cursor.