Helen: configuration files

[achirkin]

At this moment helen configuration is spread in different places, and is not really usable. We need to put all the configs in a single place. We need to make sure helen runs robustly; thus, it is rather big task.

File: helen-config.yaml, overridden by default (embeded) empty configuration. Example:

general:
  host: ip address
  port: 7654
  loglevel: warn
  logfile: filename.log (if not specified, send logs to std)
  service-restart-attempts: 10

trusted-clients:
  - 127.0.0.1
  - 129.132.32.138
  - ...

bundled-services:
  - siren:
      executable: siren.exe
      args: ...
  - another-service:
      executable: its-exe.exe
      args: cool-arg=4 ...

• [ ] Default values for general section can be taken from current defaults
• [ ] Merging configuration with default configuration should be preserved as it is now (and ideally with env variables too)
• [ ] Ideally the whole checking should not ever fail only fallback to defaults with logged warnings
• [ ] Should use monad logger to log errors/warnings
• [ ] Need to implement and test: if one of the bundled services crashes, helen should try to restart it service-restart-attempts with all proper errors logged
• [ ] Test whole configuration helen+siren+hs-example-service (either manually or set up test suite)

[NorfairKing]

Thanks for assigning me, this looks fun!

[achirkin]

Looks good, thanks!