Nomis: DSOS-2093: monitoring improvements v2

[drobinson-moj]

More tidy up of monitoring stuff as functionality was a bit muddled across roles

• Add amazon-cloudwatch-agent-collectd role which enables cloudwatch to use collectd metrics. Puts the config in the correct place, no need to run ctl commands. Use handlers properly to reload service
• Fixed selinux rules in collectd role. Removed the 5 minute wait for RHEL6. Only update if there has been a change.
• Improved collectd-service-metrics which will monitor any service using whatever shell cmd you want. Removed the other crap in there like nomis monitoring. This will go elsewhere in a separate PR. Ensure the script is reloaded if there is a change.

Tested against RHEl6,7,8,OL8 and verified metrics with this code match the old code

[jnqn]

lgtm 👍