Previously, when using PCR reader catalog its was possible to hit "PCR
reader timestamp has moved forward" when attempting to execute
workloads. This was because internal executors are exempt from the AOST
timestamp. To address this, the authentication code paths are updated to
set fixed timestamps, when connecting to a PCR reader catalog.
Additionally, additional tests are added for validating opening new
connections and preparing queries to confirm this problem is fixed.

Fixes: cockroachdb#135829

Release note: None

This patch adds a flag to the kv workload which elides preparing writing stmts
in the kv workload. This flag will be used to run workloads on read from
standby tenants in pcr tests. This flag is needed to begin the kv100 workload
on the reader tenant becase:
 - preparing a writing stmt returns an error on during reader tenant
   connection aquisition.
 - Before this patch, the kv workload driver always prepared writing statments,
   even if kv100 was initialized.
-  If all reader conn's errored during acquisition, no workload could run on
   the reader tenant.

Informs: cockroachdb#135829

Release note: none

This patch teaches the c2c roachtest driver to create a standby reader tenant
and run a workload on it. These tools are then used to spin up a kv100 workload
on the reader tenant in the c2c/kv0 roachtest.

Epic: none

Release note: none