Fold query-builder-bwc into full-cluster-restart

[nik9000]

It looks to me like qa/query-builder-bwc's tests could run along with qa/full-cluster-restart. Could we fold those two projects together to save booting all the clusters once?

[elasticmachine]

Pinging @elastic/es-search-aggs

[martijnvg]

@nik9000 👍Just moving QueryBuilderBWCIT.java to qa/full-cluster-restart module should just work.

[nik9000]

I did this in #30979.