Logstash health status hardcoded to "green"

[andsel]

Problem statement

Logstash node info API return a status which is always green because it's hardcoded value:

logstash/logstash-core/lib/logstash/api/commands/default_metadata.rb

Line 31 in fde473d

:status => "green", # This is hard-coded to mirror x-pack behavior

.

The node info status color should be one of green, yellow and red as already defined for pipeline (#14602) and queue (#11937) status.

• green: Logstash is up and running, ready to process or already proicessing data, also all pipelines are green.
• yellow: any of the pipelines is yellow, the system can still process data but it's not in ideal status. A low space condition on disk (PQ, DLQ and log files needs it) is also a yellow flag. For example if any of the partitions that Logstash is using for his duties, to store PQ segments or anything else is under a certain ration (say 70%) it could be considered yellow. It's also in yellow during the bootstrap of the process till not yet ready to process incoming data.
• red: means Logstash is up but for any motivation is not able to process data on any of its pipelines.

[andsel]

Closed by #16520