To enable prefetch, a connection configuration string is used, setting prefetch as available along with a connection default. This connection default can be overridden by a session configuration string.
For example:
conn_cfg - prefetch=(available=true,default=false) sets prefetch as available, connection default disables prefetch
session_cfg - prefetch=(enable=true) enables prefetch, overrides the connection default

From WT-16885, a bug in WT has been found, where prefetch isn't being enabled as expected during session open.
Specifically:
When the session config isn't NULL and doesn't specify prefetch, the connection default is always overridden to disable prefetch (If the session config isn't specified, the default should be used).
If the session configuration is NULL, then the connection default is never used (Session config being NULL counts as the session config not being specified, so the default should be used).

The aim of this ticket is to fix this bug, so that prefetch can be enabled as expected. and it can be used on the server side.

Definition of done:

• Prefetch is enabled/disabled as expected.
• Prefetch enabling has tests which ensure it works as intended