samples/zoap_server: Add support for the '/separate' resource
samples/zoap_server: Add support for the '/separate' resource

This resource is used to verify that the CoAP server is able to send
responses in two steps: 1. only acknowledge that the request was
received and is going to be handled; 2. The actual response, with the
payload.

Change-Id: Ia77cc0ee9805e6cc120c57f4598c68ad364882a0
Signed-off-by: Vinicius Costa Gomes <540a5b73c8ed8ee3381dfb54c1949e767fadd754@intel.com>

kraj/zephyr,runchip/zephyr-cc3200,aceofall/zephyr-iotos,galak/zephyr,rsalveti/zephyr,GiulianoFranchetto/zephyr,bigdinotech/zephyr,zephyriot/zephyr,finikorg/zephyr,bigdinotech/zephyr,GiulianoFranchetto/zephyr,sharronliu/zephyr,kraj/zephyr,punitvara/zephyr,sharronliu/zephyr,mbolivar/zephyr,fractalclone/zephyr-riscv,aceofall/zephyr-iotos,pklazy/zephyr,galak/zephyr,holtmann/zephyr,finikorg/zephyr,bboozzoo/zephyr,erwango/zephyr,explora26/zephyr,punitvara/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,runchip/zephyr-cc3220,aceofall/zephyr-iotos,runchip/zephyr-cc3200,GiulianoFranchetto/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,bigdinotech/zephyr,sharronliu/zephyr,bigdinotech/zephyr,Vudentz/zephyr,runchip/zephyr-cc3200,mbolivar/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,tidyjiang8/zephyr-doc,runchip/zephyr-cc3200,mbolivar/zephyr,zephyriot/zephyr,tidyjiang8/zephyr-doc,mbolivar/zephyr,runchip/zephyr-cc3220,ldts/zephyr,Vudentz/zephyr,explora26/zephyr,fbsder/zephyr,nashif/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,rsalveti/zephyr,ldts/zephyr,fbsder/zephyr,erwango/zephyr,runchip/zephyr-cc3220,rsalveti/zephyr,tidyjiang8/zephyr-doc,Vudentz/zephyr,tidyjiang8/zephyr-doc,holtmann/zephyr,holtmann/zephyr,galak/zephyr,aceofall/zephyr-iotos,fractalclone/zephyr-riscv,holtmann/zephyr,punitvara/zephyr,fractalclone/zephyr-riscv,punitvara/zephyr,bboozzoo/zephyr,explora26/zephyr,bboozzoo/zephyr,galak/zephyr,bboozzoo/zephyr,Vudentz/zephyr,pklazy/zephyr,bigdinotech/zephyr,fbsder/zephyr,pklazy/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,GiulianoFranchetto/zephyr,sharronliu/zephyr,fbsder/zephyr,kraj/zephyr,pklazy/zephyr,kraj/zephyr,finikorg/zephyr,tidyjiang8/zephyr-doc,bboozzoo/zephyr,rsalveti/zephyr,rsalveti/zephyr,nashif/zephyr,mbolivar/zephyr,fbsder/zephyr,sharronliu/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,fractalclone/zephyr-riscv,erwango/zephyr,galak/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,fractalclone/zephyr-riscv,punitvara/zephyr,explora26/zephyr,finikorg/zephyr,zephyriot/zephyr,erwango/zephyr,aceofall/zephyr-iotos,zephyriot/zephyr,runchip/zephyr-cc3200,erwango/zephyr,pklazy/zephyr