Support for cluster search

[pdelewski]

Routing without index at the beginning "/_search" represents cluster search.

https://github.com/QuesmaOrg/poc-elk-mitmproxy/blob/main/quesma/quesma/router.go#L20
Currently hardcoded index name as index is not part of url (As written above, that's cluster search).

It means that as a result there should be build select statement that contains more than one table in from clause,
for instance SELECT * FROM "verse-logs", "logs-generic-default";

We don't handle such case correctly. I tried to hack it https://github.com/QuesmaOrg/poc-elk-mitmproxy/compare/main...pdelewski-cluster-search, but I'm afraid we came to some limitations of our query translator and supporting this case requires redesign.