Fix to have link to prerelease docs (#1683)

* Fix aliases

* Add 1.8 prerelease page

Author: cwickham

docs/download/prerelease.qmd

@@ -18,7 +18,7 @@ anchor-sections: false
 editor: source
 image: /images/hero_right.png
 aliases:
-  - changelog/1.7/
+  - changelog/1.8/
 ---
 
 ::: {.content-visible when-profile="prerelease"}

docs/download/release.qmd

@@ -17,7 +17,7 @@ anchor-sections: false
 editor: source
 image: /images/hero_right.png
 aliases:
-  - changelog/1.6/
+  - changelog/1.7/
 ---
 
 {{< include _download.md >}}

docs/prerelease/1.8/_highlights.qmd

@@ -0,0 +1 @@
+You can view (in-progress) documentation for the next version of Quarto, v1.8, on our pre-release documentation site, [prerelease.quarto.org](https://prerelease.quarto.org), including a list of [highlights](https://prerelease.quarto.org/docs/prerelease/1.8/).

docs/prerelease/1.8/index.qmd

@@ -0,0 +1,9 @@
+---
+title: Quarto 1.8 Pre-Release
+date: last-modified
+search: false
+---
+
+{{< include _highlights.qmd >}}
+
+See the [Pre-Release Download Page](/docs/download/prerelease.qmd) for a complete list of all the changes and bug fixes.