docs: update docs header (#826)

#570

Updates the docs header to match the new design

## Demo

https://cryoet-docs-header.vercel.app/

<img width="1728" alt="image"
src="https://github.com/chanzuckerberg/cryoet-data-portal/assets/2176050/9a26c29f-4e47-4203-9e42-3ab0bdcfa975">

docs/_templates/layout.html

@@ -118,19 +118,22 @@
     <!-- top 48px for navbar height -->
     <div class="navbar-cet">
         <div style="padding: 0 16px; display: flex; height: inherit; align-items: center; justify-content: space-between;">
-            <span style="display:flex; gap: 32px; align-items: center;">
-                <a href="https://www.czimaginginstitute.org/">
-                  <img src="{{ pathto('_static/img/czi-imaging-institute.png', 1) }}" style="height: 45px; width: 45px;" />
-                </a>
-                <span style="display:flex; gap: 16px;">
-                    <span class="navbar-cet-link">
-                      <a class="navbar-cet-anchor" href="index.html">CryoET Data Portal | Documentation</a>
-                  </span>
-                </span>
+            <span style="display:flex; gap: 8px; align-items: center;">
+              <a href="index.html" style="color: #fff">CryoET Data Portal</a>
+              <img alt="beta" src="{{ pathto('_static/img/beta.svg', 1) }}">
+              <div style="width: 1px; height: 16px; background: #999; margin: 0 4px"></div>
+              <span style="color: #fff">Documentation</span>
             </span>
 
             <span class="navbar-cet-link">
-              <a class="navbar-cet-anchor" href="https://cryoetdataportal.czscience.com/">CryoET Data Portal</a>
+              <a
+                class="navbar-cet-anchor"
+                href="https://cryoetdataportal.czscience.com/"
+                target="_blank"
+                rel="noopener"
+              >
+                Go to CryoET Data Portal
+              </a>
             </span>
         </div>
     </div>