Add global description

Add global description

Add global description (info/description) to OpenApi that
states that we are providing full API for configurational
data because only those can be edited (by POST, PUT, PATCH,
DELETE) and for operational we only provide GET API.

In addition, for majority of request user can see only
config data in examples. That’s because we can show only one
example per request.

The exception when user can see operational data in example
is when data are representing operational (config false)
container with no config data in it.

JIRA: NETCONF-1138
Change-Id: I5c9de0c8780289f4557c7ce9995b8cb5d44e0290
Signed-off-by: lubos-cicut <lubos.cicut@pantheon.tech>