[Filter] Filter on "Observable" meta type

[Lhorus6]

Use case

We can't filter on "Entity type: Observables" as we used to be able to do. This was useful for:

• Share Observables via Live stream/TAXII/etc.
• Create playbooks that listen to Observables,
• Any use case that requires filtering for all Observable types

Current Workaround

It used to be possible to filter on "entity type: Observable", but this is no longer the case. You have to select all observable types (the list is long) to be able to do the same thing now.

Proposed Solution

Reimplement the ability to filter on the "Observable" meta type.

[annoyingapt]

Normally you share indicators via taxii as observables don't have a validity dates and revoke flag.

[Lhorus6]

If it's what's commonly known as IOCs that you want to share, they are indeed "Indicators". However, it's possible to have use cases where it's the Observables you want to act on/share.