fix: add page title to <title> tag if possible

[azu]

This PR make <title> to "{pageTitle} | {siteConfig.title}" if pageTitle is defined.

Node.js
http://localhost:3000/en/

About | Node.js
http://localhost:3000/en/about/

Download | Node.js
http://localhost:3000/en/download/

Documentation | Node.js
http://localhost:3000/en/docs/

Get involved | Node.js
http://localhost:3000/en/get-involved/

Node.js
http://localhost:3000/en/blog/

Node v19.8.0 (Current) | Node.js
http://localhost:3000/en/blog/release/v19.8.0

fix #5141

[azu]

📝 Some page's ${pageTitle} is "Node.js" and I avoid "Node.js | Node.js".

• http://localhost:3000/en/: { pageTitle: 'Node.js', siteConfigTitle: 'Node.js' }
• http://localhost:3000/en/blog/: { pageTitle: 'Node.js', siteConfigTitle: 'Node.js' }

[ovflowd]

I think this is extra logic. Only the pageTitle should be updated.

[azu]

closed by #5143

[ovflowd]

@azu thank you anyways for the contribution! You beat me to it, but I appreciate anyways for your effort!