Add description of COMPONENT_INIT_ONCE TO Legato documentation.
Add description of COMPONENT_INIT_ONCE TO Legato documentation.

Resolves: LE-12507
Change-Id: I42a5d15f4a514b800f0ca8b4679f810347a80f2e

legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af