Use meta variables for all doc URLs to avoid obsolete links

[yebai]

Let us create a Quarto meta variable for each doc page in a similar way to:

docs/_quarto.yml

Lines 163 to 164 in 20209fe

	get-started: docs/tutorials/docs-00-getting-started/
	tutorials-intro: docs/tutorials/00-introduction/

Usage example:

docs/404.qmd

Line 7 in 20209fe

You may want to visit [Get-Started Guide]({{< meta get-started >}}) or [Tutorials]({{< meta tutorials-intro >}}).

to avoid the fragility of relative URLs when renaming and moving doc pages.