Default YARA Dispatch Enhancements

[malvidin]

I recommend commenting out the olepackagestream and xor dispatcher rules from the default YARA rules, unless those plugins are added to this repository.

https://github.com/PUNCH-Cyber/stoq-plugins-public/blob/8aaf3b97dc3972ca852d2a73a7899afa7394f9bb/yara/yarascan/rules/dispatcher.yar#L56 https://github.com/PUNCH-Cyber/stoq-plugins-public/blob/8aaf3b97dc3972ca852d2a73a7899afa7394f9bb/yara/yarascan/rules/dispatcher.yar#L135

Adding a YARA rule for SMTP dispatching would be nice, like the following:

rule smtp_message
{
    meta:
        plugin = "smtp"
        save = "True"
    strings:
        $crlf2 = { 0D 0A 0D 0A} 
        // Values required in the email header
        $hdr_subject = "\nSubject:" nocase
        $hdr_received = "\nReceived:" nocase
    condition:
        for all of ($hdr_*) : ( @[1] < @crlf2[1] )
} 

I can put together a pull request if this is one or more of those changes should happen.