Related issue: #830

This PR aims to introduce a new option that will allow defining custom output formats for different targets in the same <localfile> stanza.

<localfile>
  <log_format>syslog</log_format>
  <location>/var/log/syslog</location>
  <target>agent,socket</target>
  <out_format target="socket">$(timestamp %Y-%m-%dT%H:%M:%S): $(log)</out_format>
</localfile>

Added options

Attribute target for option <out_format> in <localfile> stanzas.

<out_format target="custom">custom: $(log)</out_format>
<out_format target="agent">(agent): $(log)</out_format>

This attribute is optional. If it is not defined it will affect all the <target> stanzas except those that have a custom option <out_format> defined.

Unit tests

• Define <out_format> with default target for some localfiles.
• Declare <out_format> for the target "agent".
• Create <out_format> for a custom socket target.
• Combine <out_format> with a default option and another stanza for a custom socket target.
• Use <out_format> in localfile stanzas with wildcards (define the option before the location).
• Use <out_format> in localfile stanzas with wildcards (define the option after the location).
• Run Logcollector with Valgrind.
• Declare <out_format> for a target that does not exist.