[Fleet] Add a fleet_admin user and a role with the required permission for fleet.

[ph]

Add a few fleet_admin user and a role with the required permission to manage fleets related data.
We will need to add that to Elasticsearch in https://github.com/elastic/elasticsearch/blob/fa4869a94b57988912b32a0f755dd1d026eb7066/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authz/store/ReservedRolesStore.java#L51

@nchaulet or @jen-huang Could you complete this issues with a description of the permission required for the role?

@ycombinator already done it previously so we can ping him for tips if needed.

[elasticmachine]

Pinging @elastic/ingest (Feature:Fleet)

[ruflin]

Based on our more recent change that we create this ad hoc, I assume we don't need the user in ES anymore. Closing this for now. @nchaulet Please reopen if you see this differently.