We were applying the low-memory system patch to webpack.config.js
on systems with < 4GB memory.
From now on, we also let people force-enable patching by toggling the
`matrix_client_element_container_image_self_build_low_memory_system_patch_enabled`
variable.
Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1357
