For years the Ruby interpreter has been dynamically loaded with
jemalloc by using `LD_PRELOAD` to replace the system's malloc calls.
While this makes it possible to disable jemalloc, some anti-virus
scanners flag this behavior and abort the Ruby interpreter.

Since jemalloc has:

1. Significantly improved memory usage
2. Is compiled with the default for Cloud Native GitLab images
3. Is compiled with the default for all GitLab CI images

We should enable by this default and deprecate the configuration
variable.

To do this, we need to install all jemalloc files, not just the
library and binary files.

We also need to pass `-Wl,--no-as-needed` as a linker argument
due to https://bugs.ruby-lang.org/issues/18409.

Relates to #4357

Changelog: changed