feat: tidy up the tutorials navigation

[honzajavorek]

• I removed the PHP section containing a sole article. The article is about using the Apify API from PHP, so I've put it inside the Apify API section. I keep the slug untouched to avoid unnecessary redirects for now. I redirect the root of the former PHP section directly to this article, but not permanently, in case we would like to have the section back again in the future.
• I changed the titles and H1s of the section and index pages so that they're consistent. In titles, which are displayed on Google search results, I wanted to have the "tutorials" word included, but in H1s, which are displayed in the context of the navigation and docs UI, I opted for a more brief heading.
• The articles in the Apify API section seem to be assorted, so I removed sidebar_position: from their meta.
• "Apify scrapers" felt very vague, so I changed it to "Tutorials on ready-made Apify scrapers", which is what the section is actually about.

I thought I could have a single section for Apify stuff in the tutorials, where I'd move the https://docs.apify.com/academy/running-a-web-server page, but the "Tutorials on ready-made Apify scrapers" section is too self-contained and the intro expects certain contents and ordering. I don't know exactly yet what I'll do with it, but this PR feels like a good first step, groundworks for further changes.

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[apify-service-account]

Preview for this PR was built for commit ac70163 and is ready at https://pr-1873.preview.docs.apify.com!

[apify-service-account]

Preview for this PR was built for commit 9ae5e9b and is ready at https://pr-1873.preview.docs.apify.com!

[TC-MO]

LGTM, I appreciate the cleanup thank you!

[honzajavorek]

Should I wait for @metalwarrior665's eyes and a seal of approval, or just ping him for awareness?

[TC-MO]

I think it's not super urgent or anything, it can wait :)

[metalwarrior665]

Thanks, definitely an improvement. I think the Apify Scrapers might be good candidates to remove eventually, the articles are not complete (missing Playwright and Camoufox) and the Actors have really good readme. We could just change it to a single page that will list an updated list of generic scrapers. cc @nicklamonov

[honzajavorek]

Thanks! The thing about relying more on the READMEs of the scrapers makes sense! I'll keep this in mind. Or better, I'll file an issue as I might forget about this in a month or two.