A11y(docs): Ensures select element has an accessible name. and Ensure links are distinguished from surrounding text in a way that does not rely on color (#20715)

Fix 2 A11y bugs listed in title

[AB#7613](https://dev.azure.com/fluidframework/235294da-091d-4c29-84fc-cdfc3d90890b/_workitems/edit/7613)

![image](https://github.com/microsoft/FluidFramework/assets/107130183/64f80fa8-5d87-4941-81f9-342a76ef840a)

Author: RishhiB

docs/config.yml

@@ -64,7 +64,7 @@ params:
     version: "0.50"
     urlRef: "docs/updates/v0.50.md"
     message: | # if set, this will override the release notes updates
-      Fluid Framework 2.0 preview is available now! <a href="https://aka.ms/fluid/preview_blog"> Learn more.</a>
+      Fluid Framework 2.0 preview is available now! <a href="https://aka.ms/fluid/preview_blog"><u>Learn more.</u></a>
 
 menu:
   main:

docs/themes/thxvscode/layouts/partials/apiNav.html

@@ -151,7 +151,7 @@
                 aria-label="Current Page: API Overview" {{ end }}>API Overview</a>
         </li>
         <li>
-            <select name="API version" id="api-version" onchange="window.location.href = this.value;">
+            <select name="API version" aria-label="API version" id="api-version" onchange="window.location.href = this.value;">
                 {{ range $name, $version := $.Site.Data.versions.apiVersionOptionName }}
                     {{ $path := printf "%s%s/" $.Site.Data.versions.apiDocsDirectory $version }}
                     {{ $isCurrentVersion := strings.Contains $version $selectedApiVersion }}