feat(ns-api): add update-timezone script for post-commit processing

[m-dilorenzi]

This pull request adds timezone update functionality to the ns-api package. The main change is the introduction of a new post-commit hook script that updates the system timezone when relevant configuration changes are detected. Additionally, the installation process is updated to include this new script.

Timezone update feature:

• Added new post-commit hook update-timezone.py to update the /etc/localtime symlink and /tmp/TZ variable when system timezone or zonename changes are detected. (packages/ns-api/files/post-commit/update-timezone.py)
• Modified the installation process in the Makefile to install the new update-timezone.py script as part of the post-commit hooks. (packages/ns-api/Makefile)

Closes: #1454