shared/pager: add support for more(1) pager in secure mode (#41503)

The more(1) pager (part of util-linux) now supports secure mode,
which can be enabled with the MORESECURE environment variable.

Adding support for more(1) in secure mode serves as an alternative
for systems that do not have less installed or for users who prefer
it.

Commit d2fce960f9cac740 introduced secure mode in more(1) and the
new feature is available in version 2.42 of util-linux.