cortex: Add config option to set tlp value

[Jack28]

Before tlp was fixed to 'green'.

Now the analyzer config for cortex has an option to specify which tlp level to use when submitting to cortex.

[Jack28]

I would even argue to make TLP:RED the default.

Not for disclosure, restricted to participants only.

Sources may use TLP:RED when  information cannot be effectively acted upon by additional parties, and  could lead to impacts on a party's privacy, reputation, or operations if  misused.

In email it's a private conversation between a usually very limited number of entities. Nobody else should have access to the contents and attachments

[michaelweiser]

Well that's the difference between what users intend their emails to be (private) and what they technically are (public - think port 25 submission via Internet cafe Wifi). If they were to be private, they'd be encrypted. I agree, I'm nitpicking here. ;->

The commit message could still use some rationale regardless, IMO.