bosh Upgrading NATS to a supported version

Updated NATS to a supported version: 2.8.3
NATS 2.8.3 does not support wildcards in the users authorization section in the nats.cfg file. Wildcards were used previously to allow any bosh agents to publish/subscribe to NATS. Because of the new wildcards restrictions we need to add all the users explicitly in the configuration and that needs to be done continuously, as more VMs/Agents are added. To execute this continuous synchronization, we created the ruby gem 'bosh-nats-sync' which keeps the list of active agents up to date.
Added the monit infrastructure to start the bosh-nats-sync gem.

What tests have you run against this PR?

The BOSH Director unit tests.

How should this change be described in bosh release notes?

This is an update of NATS. This component used by the director was in an unsupported version.

Does this PR introduce a breaking change?

No, this won't affect users using BOSH with a standard NATS installation. Warning: For BOSH installations with custom NATS configurations (e.g custom NATS server running outside of the director VM) the bosh-nats-sync component needs to be configured and run according to the customizations.

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Co-authored-by: Brian Upton [email protected] Co-authored-by: Seth Boyles [email protected] Co-authored-by: Brian Cunnie [email protected] Co-authored-by: Manuel Alba [email protected] Co-authored-by: Long Nguyen [email protected] Co-authored-by: Daniel Felipe Ochoa [email protected]