Previously custom realms were limited in what services and components
they had easy access to. It was possible to work around this because a
security extension is packaged within a Plugin, so there were ways to
store this components in static/SetOnce variables and access them from
the realm, but those techniques were fragile, undocumented and
difficult to discover.

This change includes key services as an argument to most of the methods
on SecurityExtension so that custom realm / role provider authors can
have easy access to them.

Resolves: elastic#48369