Create a Commands Service

[drasko]

FEATURE REQUEST

1. Is there an open issue addressing this request? If it does, please add a "+1" reaction to the
   existing issue, otherwise proceed to step 2.

2. Describe the feature you are requesting, as well as the possible use case(s) for it.
   Commands service is a dedicated service to store and send commands at a given time interval. It's like a Cron of Mainflux.

Service like this would be useful in both Cloud and on the Edge:

• In the Cloud it would be programmed to send a command to the Agent (which will be executed immediately upon reception)
• On the Edge it would be programmed via Agent, and then do Command execution in the programmed period

3. Indicate the importance of this feature to you (must-have, should-have, nice-to-have).
   Should-have

[manuio]

@drasko Why not Cron service?

[drasko]

We need an external API to configure commands remotely. Also I expect this to hold some Mainflux-specific info (for example - on the gateway it has to interface with NATS and send messages respecting our protocol, and so on...)

[manuio]

@drasko I meant why not Cron Service instead of Commands Service?

[drasko]

It is a Mainflux command scheduler, not a Cron replacement.