Allow connectAttributes to be set through URI config

[mamof]

No description provided.

[sidorares]

hey @mamof , not sure about key:value pair encoding, maybe we should be consistent with how for example ssl option is passed to connection string:

mysql://username:[email protected]/dbname?ssl={"rejectUnauthorized":true}

Maybe just JSON.stringify()? mysql://username:[email protected]/dbname?ssl={"rejectUnauthorized":true}&connectAttributes={"program_name":"testProg","second_attr":"example"}