[Doc] Make front page images non clickable (#32738)

A Sphinx issue automatically makes images clickable whenever they're scaled (see https://stackoverflow.com/questions/40096251/disable-click-behavior-for-images). Clicking takes you to a full size version of the image.

On the front page of the docs, there are four prominent images that look like buttons. The user would expect clicking them to take you to a docs page, but instead it just takes you to the image. (See the linked issue for details)

Since there's no single docs page corresponding to each of these four images, in this PR we opt to make these images non clickable.

doc/source/index.md

@@ -9,7 +9,7 @@
 :card:
 
 ---
-<img src="images/getting_started.svg" alt="getting_started" height="40px">
+<img src="images/getting_started.svg" alt="getting_started" height="40px" class="no-scaled-link">
 
 **Getting started**
 ^^^^^^^^^^^^^^^
@@ -22,7 +22,7 @@ Learn how to install Ray, compute an example with the Ray Core API, and use Ray'
 {link-badge}`ray-overview/getting-started.html,"Getting started",cls=badge-light`
 
 ---
-<img src="images/user_guide.svg" alt="user_guide" height="40px">
+<img src="images/user_guide.svg" alt="user_guide" height="40px" class="no-scaled-link">
 
 **User guides**
 ^^^^^^^^^^^
@@ -38,7 +38,7 @@ Learn about the key concepts and features. Get in-depth information about Ray's
 {link-badge}`ray-core/user-guide.html,"Core",cls=badge-light`
 {link-badge}`cluster/running-applications/index.html,"Clusters",cls=badge-light`
 ---
-<img src="images/api.svg" alt="api" height="40px">
+<img src="images/api.svg" alt="api" height="40px" class="no-scaled-link">
 
 **API reference**
 ^^^^^^^^^^^^^
@@ -51,7 +51,7 @@ The reference assumes familiarity with the key concepts.
 {link-badge}`ray-references/api.html,"API reference",cls=badge-light`
 
 ---
-<img src="images/contribute.svg" alt="contribute" height="40px">
+<img src="images/contribute.svg" alt="contribute" height="40px" class="no-scaled-link">
 
 **Developer guides**
 ^^^^^^^^^^^^^^^