filter_lua: allow a config option to provide the full lua script in the config file

[ridwanmsharif]

Is your feature request related to a problem? Please describe.
Right now when using lua filters in the Ops Agent, we need to package the agent with the scripts and maintain several lua files in different locations for different distros (windows, linux). It would be easier if we could just provide the lua script contents int he config file, seeing as though most lua filter scripts are very small (roughly 10 lines).

[patrick-stephens]

See #5302

[patrick-stephens]

I'm going to add a smoke test for this but it is working with master images, YAML config is nicer for multiline:

service:
    flush:           1
    daemon:          off
    log_level:       info

pipeline:
    inputs:
        - random:
            tag:           test
            samples:       10

    filters:
        - lua:
            match:         "*"
            call:          append_tag
            code:          |
                function append_tag(tag, timestamp, record)
                   new_record = record
                   new_record["tag"] = tag
                   return 1, timestamp, new_record
                end

    outputs:
        - stdout:
            match:         "*"

Classic config:

[SERVICE]
	flush 1
	daemon off
	log_level debug
	
[INPUT]
	Name random
	Tag test
	Samples 10

[FILTER]
	Name Lua
	Match *
	call append_tag
	code function append_tag(tag, timestamp, record) new_record = record new_record["tag"] = tag return 1, timestamp, new_record end

[OUTPUT]
	Name stdout
	Match *