Add multiple tactics to ATT&CK mappings

[rw-access]

Once elastic/kibana#69166 merges, we'll be able to map tactics -> techniques with a many-many relationship. This will let us map rules to tactics without requiring a technique, and will give us better control over the relationships. We'll be able to express relationships like this:

• Privilege Escalation, Persistence
  • New Service
  • Scheduled Task
• Execution
  • Service Execution
• Lateral Movement

We need to:

1. update the schema
2. add tactics to rules that are missing one because they don't use a specific technique
3. find other cases where we can add more techniques/tactics or improve rule.threat in other ATT&CK related ways

[rw-access]

I think optional techniques gives us enough flexibility.
I'm going to close this, since it's good enough IMO