Update external_links.js to fix link behavior on MASVS page

[rmRizki]

When you open https://mas.owasp.org/MASTG/ you will notice that external links (like github repo for example) will have small arrow icon and _blank attribute that will open the link in the new tab. But https://mas.owasp.org/MASVS/ page doesn't have the same behavior.

This PR modifies the code to enhance the user experience on the MASVS page (https://mas.owasp.org/MASVS/) by ensuring that external links open in a new tab, similar to the behavior on the MASTG page (https://mas.owasp.org/MASTG/).

This change involves updating the checking if the path starts with '/MASTG' or '/MASVS' and applying the necessary attributes to external links accordingly. It also add document$.subscribe() so the code still executed when page navigate (reference: squidfunk/mkdocs-material#5816)

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[cpholguera]

Thanks @rmRizki, we'll take a look soon!

[cpholguera]

Excellent work @rmRizki, thank you very much!