25014: storage: queue requests to push txn / resolve intents on single keys r=spencerkimball a=spencerkimball

Previously, high contention on a single key would cause every thread to
push the same conflicting transaction then resolve the same intent in
parallel. This is inefficient as only one pusher needs to succeed, and
only one resolver needs to resolve the intent, and then only one writer
should proceed while the other readers/writers should in turn wait on
the previous writer by pushing its transaction. This effectively
serializes the conflicting reader/writers.
    
One complication is that all pushers which may have a valid, writing
transaction (i.e., `Transaction.Key != nil`), must push either the
conflicting transaction or another transaction already pushing that
transaction. This allows dependency cycles to be discovered.

Fixes #20448 

25791: jobs: bump default progress log time to 30s r=mjibson a=mjibson

The previous code allowed updates to be performed every 1s, which could
cause the MVCC row to be very large causing problems with splits. We
can update much more slowly by default. In the case of a small backup
job, the 5% fraction threshold will allow a speedier update rate.

Remove a note that's not useful anymore since the referred function
can now only be used in the described safe way.

See #25770. Although this change didn't fix that bug, we still think
it's a good idea.

Release note: None

26293: opt: enable a few distsql logictests r=RaduBerinde a=RaduBerinde

 - `distsql_indexjoin`: this is only a planning test. Modifying the
   split points and queries a bit to make the condition more
   restrictive and make the optimizer choose index joins. There was a
   single plan that was different, and the difference was minor (the
   old planner is emitting an unnecessary column).

 - `distsql_expr`: logic-only test, enabling for opt.

 - `distsql_scrub`: planning test; opt version commented out for now.

Release note: None

Co-authored-by: Spencer Kimball <spencer.kimball@gmail.com>
Co-authored-by: Matt Jibson <matt.jibson@gmail.com>
Co-authored-by: Radu Berinde <radu@cockroachlabs.com>