GraphQL CQL-first: bulk insert does not handle conditional batch

[olim7t]

Disclaimer: the query is convoluted, I'm not sure if there's any realistic use case.

CQL:

create table foo(k int primary key, v int);
insert into foo(k,v) values(1,1);

GraphQL:

mutation @atomic {
  bulkInsertfoo(values: [{ k: 1, v: 2 }, { k: 1, v: 3 }], ifNotExists: true) {
    applied
    value {
      k
    }
  }
  insertfoo(value: { k: 1, v: 4 }, ifNotExists: true) {
    applied
    value {
      v
    }
  }
}

This causes:

java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
        at io.stargate.graphql.schema.cqlfirst.dml.fetchers.DmlFetcher.toListOfMutationResults(DmlFetcher.java:122)

The methods assumes that if there are rows then it's one per input value, but if the batch is conditional, only one row is returned.

[olim7t]

Possibly a more likely use case once we fix #1069.