utilities/auto-blog-link-preserver#16: Allow script to be imported as a module

I've committed a python-sin: there's no if __name__ == '__main__' in there (because I hadn't included it in the code that I forked either).

Although not related to the container image that's being built, I'd quite like to be able to write some code to go over all existing pages on my site - essentially backfilling links.

To do that, I'll need to write a small wrapper (to generate a list of links as there's no RSS to go off) and then invoke the extraction + linkwarden functions.