Feature Request: GET/PUT endpoints for agent config + device model

[robot-ranger]

This is an issue to track the proposal of adding GET/PUT REST routings to get&set agent config as well as devices.xml

The agent currently restarts, per configuration, if the agent.json and/or devices.xml are modified on the filesystem.

these new endpoints would enable lightweight webapps for agent (re)configuration but in order to make this happen, we need to add GET and PUT endpoints for agent config as well as PUT endpoint for device model (the device model can already be retrieved at / or /probe

With the addition of agent config schema autocomplete suggestions and validation for agent config run right in the browser:

[robot-ranger]

We can display and textually edit the device model, but unfortunately Monaco Code Editor does not have built-in schema-based autocomplete suggestions for xsd like it does for json:

[robot-ranger]

as far as security, sensitive system admins should control PUT with AllowPut and AllowPutFrom config parameters