Support combined metric queries for correlation rules with LogQL

[kelnage]

When correlating multiple queries, we can do so using Loki and LogQL by generating one metric query per log query, and combining them with OR (for event_count and value_count correlation rules) or AND (for temporal correlation rules). E.g., the following log queries:

{job=`.+`} | logfmt | fieldA=`valueA`
{job=`.+`} | json | fieldB=`valueB`

can be converted into an event_count correlation query with greater than or equal to 2 events with the following LogQL:

(sum(count_over_time({job=`jobA`} | logfmt | fieldA=`valueA`[$__auto])) 
    or sum(count_over_time({job=`jobB`} | json | fieldB=`valueB`[$__auto]))) >= 2