Add setup script for 'apm-server'

[fatmcgav]

This creates a keystore for apm-server, and adds the ELASTIC_PASSWORD entry to it.
Also copies it into /config/apm-server so that it's available to the server.

Resolves #73

[fxdgear]

@fatmcgav this will get resolved in: #76

BUT I'm curious why is the apm-server binary not getting picked up in

stack-docker/scripts/setup-beat.sh

Line 5 in 7803fa0

beat=$1

We shouldn't need a new setup script.

[fatmcgav]

@fxdgear So I went with a new script as there were some subtle differences in path layouts, commands to setup dashboards etc...

Edit: Actually, the file path issue became a non-issue, but the permissions was an issue... apm-server.yml had to be owned by root to be able to progress...

[fatmcgav]

Also, when I started looking, having apm-server configured in setup-beat.sh just felt... wrong... to me... apm-server != beat???

[fxdgear]

I agree on the name bit.

Perms is kind of annoying, which is why I created my PR referenced above, but haven’t had time to dig into the last issue I ran into. :(