Improve rego-templates for OpsGenie action

[afdesk]

now vuls-opsgenie.rego contains a very simple template for OpsGenie messages.

we should add more useful details and filters that allows to transform inputs.

eg. severity depends on the result, using the users from the result (owners) etc.

@simar7 isn't it? or i miss something

[simar7]

Can you add the details to the issue description to describe what this is about?