Expose new libzim settings to handle memory consumption

[benoit74]

https://github.com/openzim/libzim/pull/950 moved some settings from env parameters to CPP exposed settings. This has been released in libzim 9.3.0.

https://github.com/openzim/libzim/pull/960, https://github.com/openzim/libzim/pull/974, https://github.com/openzim/libzim/pull/975 and https://github.com/openzim/libzim/pull/982 pushed this further by allowing to configure the memory we want to consume. This ~~is planned to be~~ has been released in libzim 9.4.0.

These settings should be exposed in libzim as well.

Should we release libkiwix without this issue handled, it means that we will introduce a kind of regression since environment variable available in the past (and used in our infra) are not here anymore, and there is no new way to do the same thing.

I will open a companion issue in kiwix-tools.

[benoit74]

Companion kiwix-tools issue is https://github.com/kiwix/kiwix-tools/issues/745