Optionally fail when a non-partition-restricted query is issued against a storage-attached index

With LCS, we will have potentially thousands of SSTables for a given user table. Storage-attached also means SSTable-attached, and searching thousands of attached indexes is not going to scale well at all locally, due to the sheer number of searches and amount of postings list merging involved. We should have a guardrail to prohibit this by default.

Partition-restricted queries, the use-case SAI is broadly designed for, should be very efficient.

UPDATE: The consensus from the discussion below is that we'll add two guardrails here. One is simply for whether we'll allow non-partition-restricted 2i queries. The other is a warn/fail threshold pair for the number of SSTable indexes read locally on a query.