Summary:
Add a new pggate metric to collect read ops.  This is separate from read
requests, which counts the number of RPC round trips.  Read ops gives
better insight into how many operations there are, unaffected by request
parallelism.  Plumb this metric up to EXPLAIN (ANALYZE, DIST) as the
following fields:

- Storage Read Ops
- Storage Table Read Ops
- Storage Index Read Ops
- Catalog Read Ops

Update test output with the new field.  Note that a yb.orig.foreign_key
regress test number is odd due to issue #28026.  For
yb.orig.index_recheck, change some primary-key-less tables to have a new
s serial primary key column to reduce flakiness on low-row-count index
scans potentially not hitting all table tablets.
Jira: DB-17649

Test Plan:
jenkins

Close: #28028

Reviewers: kramanathan, dmitry

Reviewed By: kramanathan

Subscribers: smishra, yql

Differential Revision: https://phorge.dev.yugabyte.com/D45406