[Fleet] Convert saved objects to be sharable across spaces

[jen-huang]

Kibana now has support for sharable saved objects: #27004

Existing saved object types can't take advantage of this new functionality until 8.0 due to breaking changes. Since Kibana assets installed by Fleet are things like dashboards and visualizations, which are generic Kibana SOs, I believe the Kibana team will handle the migration for those. This issue is a placeholder for the Fleet team to double-check that work and revisit Fleet-specific SOs and convert them if necessary.

See #74353 (comment) for some ideas of how this could work from a UX perspective.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[ruflin]

I assume the concept of space agnostic SO will stay around? Would there be any reason to move these to shareable?

[jen-huang]

@ruflin Yes, space-agnostic concept will still exist, but it's recommended to use a sharable type in most cases. I'm not sure if it makes sense to use sharable type for Fleet SOs, but it's something to consider now that we have this capability. I recall in the beginning we made everything agnostic for simplicity. For example, maybe certain spaces should only be able to manage certain agent policies and outputs.