This commit adds a hard requirement to the RPM and Debian packages for
/bin/bash to be present, and adds a note regarding this to the migration
docs.
Relates #18259
This commit adds a new configuration file jvm.options to centralize and
simplify management of JVM options. This separates the configuration of
the JVM from the packaging scripts (bin/elasticsearch*, bin/service.bat,
and init.d/elasticsearch) simplifying end-user operational management of
custom JVM options.