adding schema to qla filter

The query metadata captured by qlafilter does not contain the schema on which the query is done. Having this information is useful when multiple applications share a DB but are logically separated by the schema.

A solution might be to take the schema information from the connection. The only drawback here is queries where we explicitly define another schema. Example:

mysql -h host -u user -p salary

> [...] # any query gets automatically the `salary` schema

# edge case:

> select user from mysql.user;

I would be ok with the edge case not being covered.