fix confusing/misleading info about parser support in YAML config

[alexakreizinger]

bear with me... this is going to be the first PR in a series of PRs trying to clarify some confusing stuff related to parsers, processors, and other YAML configuration-related topics. but I'm starting with this because it was the tiny thread that kept unraveling the more I pulled at it.

long story short, I thought it was odd that one of the configuration file pages stated that YAML configuration files don't support parsers. then I realized that it's because YAML configuration files don't have a dedicated parsers section—which is to say, that parsers are defined on a per-plugin basis.

so this PR attempts to perform the minimum viable amount of cleanup to clear up that confusion. that said, I'm going to need to revisit some of the docs in this section to cut through other things that are potentially misleading and to consolidate duplicated/scattered info.

[cosmo0920]

I added a comment for the top level elements of YAML configuration.

[cosmo0920]

parsers can handle in YAML type of configurations:

This is an example configuration of YAML but it's still valid for the format:

env:
  FLB_ENV: "1"

parsers:
  - name: json
    format: json

plugins:
  - /opt/fluent-bit/plugins/custom.so

service:
  flush: 1
  log_level: info

pipeline:
  inputs:
    - name: tail
      path: /var/log/syslog
  outputs:
    - name: stdout

[alexakreizinger]

🤔 what does an example configuration like this do? does it apply a JSON parser to all inputs?

[cosmo0920]

I mean, parsers, multiline_parsers, and plugins are able to be handled in the same YAML configurations.
But in classix format, parsers, multiline_parsers, and plugins should be handled with parsers_file and plugins_file and loaded as separated other files.
This could be an advantage of YAML format of Fluent BIt configurations.

[alexakreizinger]

ah, that makes sense :) so those are optional sections you can use to define custom parsers/plugins/etc

of the other sections that you can include in a YAML config, are any of them required? I'm wondering if it would be helpful to specify which ones you always need to include versus which ones are optional.

[cosmo0920]

The suggested sections are all of optional. So, it's not needed to put in every configuration.

[esmerel]

one minor nit, but looks good to me
🎉 ship it