OpenAPI description should fill the field `servers`

In order to be able to spawn RPC to a tezos-node directly from the "UI" generated for the openAPI specification, the generator should add at toplevel something along the lines of

"servers": [
{
"url":"http://localhost:8732/",
"description":"localhost:8732"
}
]

(and optionally other entries with public nodes ?)

The following discussion from !4089 (closed) should be addressed:

• @NicVolanschi started a discussion: (+2 comments)

  I tried the mempool API in gitlab, but either it doesn't work or the doc seems outdated. For instance, GET /filter "minimal_fees" returns:

  "This endpoint is deprecated. Use /users/filter/activity instead."