doc: output alphabetic Kconfig options index
doc: output alphabetic Kconfig options index

Instead of a configuration options index in "discovered" order
during the walk of the Kconfig files, create the index in alphabetic
order.

Also added a more descriptive name above the displayed table and added
table headings.

jira: ZEP-2310

Signed-off-by: David B. Kinder <c56c8b29908a5b2af1b63001268d73a0b7f972ba@intel.com>

finikorg/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,Vudentz/zephyr,kraj/zephyr,aceofall/zephyr-iotos,galak/zephyr,aceofall/zephyr-iotos,ldts/zephyr,mbolivar/zephyr,explora26/zephyr,kraj/zephyr,Vudentz/zephyr,zephyriot/zephyr,kraj/zephyr,mbolivar/zephyr,finikorg/zephyr,fbsder/zephyr,rsalveti/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,explora26/zephyr,runchip/zephyr-cc3220,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,kraj/zephyr,zephyriot/zephyr,kraj/zephyr,galak/zephyr,mbolivar/zephyr,rsalveti/zephyr,zephyriot/zephyr,fbsder/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,explora26/zephyr,explora26/zephyr,ldts/zephyr,finikorg/zephyr,ldts/zephyr,mbolivar/zephyr,zephyriot/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,zephyrproject-rtos/zephyr,rsalveti/zephyr,mbolivar/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,aceofall/zephyr-iotos,nashif/zephyr,punitvara/zephyr,punitvara/zephyr,Vudentz/zephyr,galak/zephyr,fbsder/zephyr,ldts/zephyr,nashif/zephyr,aceofall/zephyr-iotos,finikorg/zephyr,zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,fbsder/zephyr,rsalveti/zephyr,runchip/zephyr-cc3220,explora26/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,rsalveti/zephyr,zephyriot/zephyr,fbsder/zephyr,galak/zephyr