tests: lwm2m: Information Reporting Interface [300-399]

Implement testcases for Information Reporting Interface [300-399]:

* LightweightM2M-1.1-int-301 - Observation and Notification of parameter
  values
* LightweightM2M-1.1-int-302 - Cancel Observations using Reset
* LightweightM2M-1.1-int-304 - Observe-Composite Operation
* LightweightM2M-1.1-int-306 – Send Operation
* LightweightM2M-1.1-int-307 – Muting Send
* LightweightM2M-1.1-int-308 - Observe-Composite and Creating
  Object Instance
* LightweightM2M-1.1-int-309 - Observe-Composite and Deleting
  Object Instance
* LightweightM2M-1.1-int-310 - Observe-Composite and modification of
  parameter values
* LightweightM2M-1.1-int-311 - Send command

303 and 305 cannot be implemented using Leshan as it only support
passive cancelling of observation.

Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no>