Better support for loghouse queries in tabbix

[z9r5]

Loghouse stores labels as mapped columns. That’s why searching by label in Loghouse applies this ClickHouse syntax:
string_fields.values[indexOf(string_fields.names, "from")] = "deploy/web"

Label value can be stored in string_fields, bool_fields, time_fields or number_fields. Tabbix has no clue about it, so we have to:

• make tabbix work with ClickHouse labels, or
• make a proxy for ClickHouse protocol that will rewrite query, or
• implement mapped columns support in ClickHouse itself.