extend intel.log with additional fields using corelight/ExtendIntel (part 1)

[mmguero]

• corelight/ExtendIntel

We could be getting more useful information from our zeek intelligence matches, and this plugin can help us do that

• add plugin to list of plugins to install
• add new fields to intel.log parsing

Splitting this into two parts, one to get the plugin integrated and the basics listed above, and another one at a future time to further expand the usage of these new fields, see #695