Add `pageBasePath` to blog plugin configuration about docusaurus

[ilg-ul]

My chronology site is Romanian only, and paths are localised, only page was in English, that's why I needed this patch.

BTW, don't get me wrong, all my other projects and sites are English only, the chronology site was an exception and I had some difficulties to localise it, since I've never done similar things before.

[ilg-ul]

Since this probably the simplest proposal, I submitted a first PR, trying to learn the process.

I'll need some help to understand how this feature can be tested. A link to a similar test would help.

[slorber]

👍 looks like a good option to add

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This feature can be useful for example when all paths are translated to local languages.

Not sure what you mean here, but we don't particularly recommend to localize paths/slugs.

https://docusaurus.io/docs/i18n/introduction#i18n-non-goals

If your site supports multiple locales, localizing urls will cause problems when switching from one locale to another.