Add support for 'size' in EQL Sample queries

[luigidellaquila]

EQL queries allow to pass a "size" parameter to limit the number of returned results:

{
  "size": 3,
  "query": "<an EQL query>"
}

This PR adds support for this parameter on Sample queries.

[elasticmachine]

Pinging @elastic/es-ql (Team:QL)

[luigidellaquila]

@elasticmachine run elasticsearch-ci/part-2

[luigidellaquila]

Sorry for the noise here, it seems after a merge from main branch GitHub is struggling to re-calculate the diff with the head branch feature/eql_samples.

The PR shows ~200 commits ahead of the feature branch, but with a manual check it's clear that all of them are already in the feature branch and that both the feature branch and the PR are up to date with main, so this behavior is unexpected, most likely related to https://github.com/isaacs/github/issues/750 and to our switch from master to main branch.

I'll give it a few hours to settle and hopefully re-calculate the diff. If it doesn't fix by itself, I'll close this and open a new PR