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:password@us-east.connect.psdb.cloud/dbname?ssl={"rejectUnauthorized":true}

Maybe just JSON.stringify()? mysql://username:password@us-east.connect.psdb.cloud/dbname?ssl={"rejectUnauthorized":true}&connectAttributes={"program_name":"testProg","second_attr":"example"}