[Accesses API] Small corrections in the API definition #152

Problem description

Three unrelated small items in code/API_definitions/dedicated-network-accesses.yaml.

1. The API-specific error code has the wrong prefix. The code is
DEDICATED_NETWORK_ACCESS.NO_VALID_DEVICE, in the singular, while the base path of this API is
dedicated-network-accesses:

servers:
  - url: "{apiRoot}/dedicated-network-accesses/vwip"

so its codes should be prefixed DEDICATED_NETWORK_ACCESSES. The current prefix appears three times:
in the code enum of the 422 response, in the name of the example
DEDICATED_NETWORK_ACCESS_422_NO_VALID_DEVICE, and in that example's code value.

2. The Location header schema has no uri format. On POST /accesses it is declared as:

            Location:
              description: 'URL including the resource identifier of the newly created network access.'
              required: true
              schema:
                type: string
                maxLength: 2048

createNetwork in code/API_definitions/dedicated-network.yaml declares the same header with
format: uri as well. Without it, a value that is not a URL is valid against the Accesses
specification even though the description says it is one. There is nothing to reference from the
common files — CAMARA_common.yaml defines x-correlator, x-total-count, x-total-pages and
link under components/headers, but no Location.

3. Two code fields are free strings. ResultForDevice.code carries the per-device outcome and
ReasonInfo.code the reason for a status change; both are type: string, maxLength: 96 with no set of
values. A consumer acting on ResultForDevice.code cannot tell what it may contain — the examples use
IDENTIFIER_NOT_FOUND and CONFLICT, and the neighbouring status description mentions 429, but
none of those is in the schema. For ReasonInfo.code a set does exist, but only where
DeviceStatusInfo narrows it to REQUEST_APPROVED, REQUEST_REJECTED, REQUEST_FAILED,
ACCESS_REVOKED and ACCESS_FAILED, so any other use of ReasonInfo would carry none. Both are
reported by CAMARA Validation on the r2.2 release-review pull request as hint S-313.

Expected behavior

1. Rename the error code to DEDICATED_NETWORK_ACCESSES.NO_VALID_DEVICE in all three places.
2. Add format: uri to the Location header schema, matching dedicated-network.yaml.
3. Give ResultForDevice.code an enum of the codes the API can return, and consider moving
   ReasonInfo's set of values onto the base schema so it holds wherever ReasonInfo is used.