Add regen all script

[jepenven-silabs]

Problem

Generating all ZCL files per example is a long and tedious task that will grow with the number of examples.

Summary of Changes

This script will generate all ZAP templates for each examples automatically. It will search for *.zap files in the examples directory and then call the zap_generate.sh script. Useful when one is modifying the zap templates and want to update all generated files at once.

Add-on to #3637

[vivien-apple]

Looks good to me. One cool thing would be to automatically call clang-format -I on the gen/ folders if clang-format is available. It allows to spot the differences much more easily.
But that's a nit since I guess this is out of scope for this PR.