Adding upper bound for number of I/O processes

We need to have a configure option to optionally add an
upper bound for the number of I/O processes in PIO.

The upper bound will override the number of I/O processes
set by the user (when it exceeds the upper bound).

Currently users can set the number of I/O tasks and I/O
stride. Setting the number of I/O tasks can limit the number
of I/O processes but having a common upper bound (that
can be configured on a per-machine basis) is useful
especially for high res runs.

Setting the upper bound is useful for machines where we
want to set the number of I/O processes close to the physical
I/O nodes on the machine. Limiting the number of I/O processes
has been useful in improving I/O performance of high res
E3SM runs in the past.