Support Optional includes in configuration file

[cintolas]

Proposed change

Currently if the include file is missing, the nats server will fail with a parse error

host: 0.0.0.0
port: $PORT
authorization: {
  token: $TOKEN
}

include ./nats-cluster.conf

PORT=4225 TOKEN="a1234" nats-server -c ~/nats/nats.conf 
nats-server: error parsing include file './nats-cluster.conf', open /home/peter/nats/nats-cluster.conf: no such file or directory

Feature Request

Add a way to specify that this include is optional

include? ./nats-cluster.conf

If the file is missing, continue

Use case

We are creating clusters where High Availability (HA) is optional.
We would like to keep the default configuration as simple as possible and allow the power users to extend the options as needed.

This will allow systemd service files to stay the same since the config file doesn't change

Contribution

No response

[wallyqs]

I like this idea, could be an alternative to always including empty files.

[jjlights]

Hi, is this proposal accepted? I would like to pick it up, looks like reasonable for flexibility and good first-issue for newcomer.

[wallyqs]

yes if you send a PR I think we can consider it

[jjlights]

sure will do

[olliehcrook]

Hey, I have raised a PR #7919 implementing this. Please let me know if there is any changes I should make 😄