Syslog input as wrapper

[djaglowski]

The syslog_input operator was previously implemented
as a builder that built two operators. While this is
a perfectly fine solution, it happens to be the only
place in this codebase where multiple operators are
returned from a builder, excepting plugins.

This new implementation builds the same two operators,
but then wraps them together within a single operator.
This will allow for the eventual simplification of
other code, once plugins are also removed from this
codebase.

Related to #375, #380

[codecov]

Codecov Report

Merging #376 (3407c28) into main (3f71d1b) will increase coverage by 0.1%.
The diff coverage is 86.5%.

@@           Coverage Diff           @@
##            main    #376     +/-   ##
=======================================
+ Coverage   77.1%   77.3%   +0.1%     
=======================================
  Files         94      95      +1     
  Lines       4471    4483     +12     
=======================================
+ Hits        3449    3467     +18     
+ Misses       702     699      -3     
+ Partials     320     317      -3     

Impacted Files	Coverage Δ
operator/builtin/parser/syslog/syslog.go	69.6% <ø> (ø)
operator/builtin/input/syslog/syslog.go	73.5% <83.3%> (+15.0%)	⬆️
operator/builtin/input/tcp/tcp.go	80.0% <100.0%> (+1.9%)	⬆️
operator/builtin/input/udp/udp.go	76.3% <100.0%> (+0.5%)	⬆️
operator/builtin/input/file/file.go	70.2% <0.0%> (-2.1%)	⬇️
operator/builtin/input/file/config.go	77.0% <0.0%> (ø)
operator/builtin/input/file/roller_other.go	100.0% <0.0%> (ø)
agent/builder.go	92.5% <0.0%> (+0.9%)	⬆️

[djaglowski]

The contrib failure is expected due to this change. I've proven out a change to syslogreceiver.DecodeInputConfig that will fix it:

// DecodeInputConfig unmarshals the input operator
func (f ReceiverType) DecodeInputConfig(cfg config.Receiver) (*operator.Config, error) {
	logConfig := cfg.(*SysLogConfig)
	yamlBytes, _ := yaml.Marshal(logConfig.Input)
	inputCfg := syslog.NewSyslogInputConfig("syslog_input")
	inputCfg.SyslogBaseConfig = syslogparser.NewSyslogParserConfig("syslog_parser").SyslogBaseConfig

	if err := yaml.Unmarshal(yamlBytes, &inputCfg); err != nil {
		return nil, err
	}
	return &operator.Config{Builder: inputCfg}, nil
}

[djaglowski]

This change ended up simplifying the syslog_input operator in some notable ways. Particularly, I like that it removed the need for a custom unmarshal function.

[jsirianni]

@djaglowski do we expect contrib-tests to fail?

[djaglowski]

@djaglowski do we expect contrib-tests to fail?

Yeah, see comment above.

[jsirianni]

I built this against my local contrib and tested TCP and UDP against rfc5424, looks good.