tail new multiline support(fluentbit must be later than V1.8)

[wenchajun]

https://docs.fluentbit.io/manual/pipeline/inputs/tail#multiline-and-containers-v1.8
If you are running Fluent Bit to process logs coming from containers like Docker or CRI, you can use the new built-in modes for such purposes. This will help to reassembly multiline messages originally split by Docker or CRI:

[INPUT]
    name              tail
    path              /var/log/containers/*.log
    multiline.parser  docker, cri

Signed-off-by: chengdehao dehaocheng@yunify.com

[wanjunlei]

It is not an appropriate practice to define MultilineParser as a string.

What if the parameter multiline.xxx is added later?

Maybe a struct is more reasonable.

type Multiline struct {
  Parser string
}

[wenchajun]

Thanks. But there is the multiline property in the old property.

	// If enabled, the plugin will try to discover multiline messages
	// and use the proper parsers to compose the outgoing messages.
	// Note that when this option is enabled the Parser option is not used.
	Multiline *bool `json:"multiline,omitempty"`

And after testing, and if a structure is added, the following input is required for the user

DB:
      sync: xx

Not like the original

dbSync: xxx

The original configuration file is more similar to fluent-bit itself