doc: add documentation for local operator console

OPERATOR_CONSOLE.md

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+# Local Operator Console (LOC) API
+
+This document explains the Local Operator Console(LOC) from the API point of view.
+
+This document is similarly structured as PROFILE.md, because the topic is very similar.
+
+## What is Local Operator Console?
+
+Local Operator Console is kind of a miniature controller that allows to run certain
+commands (see [Compound Config](###Compound-Config)) without connection to the real
+controller. One main usage is for air-gap environments, where devices are offline
+and connection to the remote controller is not available or when the connection
+to the controller is slow or lots of packets get lost.
+
+## Differences Between Local Operator Console and Local Profile Server
+
+|                                        | LOC      | LPS                |
+|----------------------------------------|----------|--------------------|
+| Can Handle more than 1 device          | Y        | N                  |
+| Uses security token for authentication | N        | Y                  |
+| Needs config from controller           | Y        | N                  |
+| Runs on                                | Edge App | Anywhere reachable |
+
+## Server endpoint
+
+EVE periodically sends a `CompoundEdgeDevConfigRequest` to the Local Operator Console.
+EVE can find the URL to the LOC in `loc_url` which is part of the
+`EdgeDevConfig` that EVE received from the controller.
+
+## Endpoints
+
+In the following `$UUID` is the uuid of the edge node contacting LOC.
+All endpoints return with `Content-Type` set to `application/x-proto-binary`.
+
+### Certs
+
+```http
+
+       GET /api/v2/edgedevice/certs
+```
+
+Returns the controller certificates as defined in `ZControllerCert` in `certs/certs.proto`
+file.  It is encapsulated in an `AuthContainer` as defined in `auth/auth.proto` file.
+The container is not verified.
+
+### Config
+
+```http
+    POST /api/v2/edgedevice/id/$UUID/config
+```
+
+Returns the signed config from the controller. It is an `config/EdgeDevConfig`
+and the definition can be found in the `devconfig.proto` file.
+
+### Compound Config
+
+```http
+    POST /api/v2/edgedevice/id/$UUID/compound-config
+```
+
+Returns the signed edge device config as part of the compound config. It also includes:
+
+* current Unix timestamp in nano seconds precision
+* device command
+* app commands
+* radio config
+
+The device command can be:
+
+* shutdown of the device
+* shutdown and poweroff of the device
+* reboot of the device
+* run collect-info and upload the tarball to the configured datastore via POST/PUT
+
+The app commands can be:
+
+* restart of the app
+* purge of the app
+
+The definition can be found as `CompoundEdgeDevConfig` in `config/compound_devconfig.proto`.
+
+### Edge Metrics
+
+```http
+    POST /api/v2/edgedevice/id/$UUID/metrics
+```
+
+This is where the metrics are sent. Similar to the controller API.
+It is a `ZMetricMsg` as defined in `metrics/metrics.proto`.
+
+### Edge Info
+
+```http
+    POST /api/v2/edgedevice/id/$UUID/info
+```
+
+This is where the info messages are sent. Similar to the controller API.
+It is a `ZInfoMsg` as defined in `logs/log.proto`.