Add ability to filter printed headers in telegraf config

[glinton]

Resolves #5584

This adds header-filter as an option to filter the printing of the global_tags and agent sections of the config file. By setting to "none", config headers will be skipped, allowing the creation of minimal config files.

$ telegraf \
  --output-filter none \
  --processor-filter none \
  --aggregator-filter none \
  --input-filter cpu \
  --header-filter none config

# Read metrics about cpu usage
[[inputs.cpu]]
  ## Whether to report per-cpu stats or not
  percpu = true
  ## Whether to report total system cpu stats or not
  totalcpu = true
  ## If true, collect raw CPU time metrics.
  collect_cpu_time = false
  ## If true, compute and report the sum of all non-idle CPU states.
  report_active = false

[danielnelson]

Would it be possible to call this --section-filter and allow it to skip the plugin sections too? So if you have telegraf --section-filter agent it only prints the agent section, and if you have telegraf --section-filter input it doesn't show the 3 line comment header for the other plugin types?

[glinton]

That would work, though I do like the ability to remove all unneeded comments in a generated file without piping to a text processor.

[danielnelson]

I think we should have this so that this command only prints the [agent] section, no inputs/outputs etc.

./telegraf --section-filter agent config

Also should support sections inputs, outputs, processors, outputs:

./telegraf --section-filter inputs:processors config

Only show the header for a section when the section is enabled.

[glinton]

Ok, now I see what you're saying. I understood the section-filter was to only control the other (currently non-configurable) sections agent, and global-tags. To just show the agent section, with changes up to now on this branch, you would need to specify:

./telegraf --section-filter agent  --input-filter none --output-filter none  --aggregator-filter none --processor-filter none config

Which is a lot of configuration. Making the change now.