Ability to set JVM arguments so they are persisted across upgrades

In order to increase the memory that Bitbucket Server uses, the admin must edit the setenv.sh script in the application install directory. Unfortunately, that means the settings must be re-applied on each upgrade. Provide a way to change the setting that will be persisted across upgrades.

Original suggestion:

It would be nice, if the setenv.sh would first check whether JVM_MINIMUM_MEMORY and JVM_MAXIMUM_MEMORY variables are set and if not, it creates with default values. This would allow to set JVM parameters in the init.d script and would ease the upgrade procedure.

Workaround
Set JVM_MINIMUM_MEMORY and JVM_MAXIMUM_MEMORY permanently as environmental variables. This will persist across upgrades without any script modification needed. This is also true for JVM_SUPPORT_RECOMMENDED_ARGS.