Improve data sustainability statement visibility

Improve the visibility of our data sustainability statement. Add
it to the index page under the vision and mission statements, as
a menu dropdown to the about menu, and to the menu representation
in the footer.

Author: clnsmth

templates/index.html

@@ -39,7 +39,25 @@
         </div>
 
         <hr style="width: 15%;">
-        
+
+        <!--data sustainability-->
+        <div class="px-4 py-1 my-0 text-center">
+            <br>
+            <a href="/about/data-sustainability" class="fw-normal hover-underline-animation" style="font-size:2em; color: rgb(36, 41, 47);">Data Sustainability</a>
+        </div>
+        <div class="px-4 py-1 my-0 text-center">
+            <div class="col-lg-6 mx-auto">
+                <p class="lead mb-4">The Environmental Data Initiative (EDI) is deeply committed to the long-term
+                    sustainability of the ecological and environmental data entrusted to our care. As our community
+                    grows, both in the diversity of scientists we serve and the increasing reliance on our data
+                    services, so too does our responsibility to ensure the enduring availability, integrity, and
+                    utility of these valuable scientific assets. Sustaining data for the long haul is central to
+                    EDI’s mission and essential to the future of science. In partnership with our funders and
+                    collaborators, we are advancing this commitment through three core operational priorities ...
+                    <a href="/about/data-sustainability">Continue reading</a>.</p>
+            </div>
+        </div>
+
         <!--what we provide-->
         <div class="px-4 py-1 my-0 text-center">
             <br>

templates/shared/layout.html

@@ -93,6 +93,7 @@
                                 </a>
                                 <ul class="dropdown-menu" aria-labelledby="navbarDropdown">
                                     <li><a class="dropdown-item" href="/about/about-edi">EDI</a></li>
+                                    <li><a class="dropdown-item" href="/about/data-sustainability">Data Sustainability</a></li>
                                     <li><a class="dropdown-item" href="/about/edi-policy">Policies</a></li>
                                     <li><a class="dropdown-item" href="/about/edi-products">Products</a></li>
                                     <li><a class="dropdown-item" href="/about/edi-public-calendar">Calendar</a></li>
@@ -199,6 +200,8 @@ <h4 class="text-white">About</h4>
                     <ul class="nav flex-column">
                         <li class="nav-item mb-2"><a href="/about/about-edi" class="nav-link p-0 text-white">EDI</a>
                         </li>
+                        <li class="nav-item mb-2"><a href="/about/data-sustainability" class="nav-link p-0 text-white">Data Sustainability</a>
+                        </li>
                         <li class="nav-item mb-2"><a href="/about/edi-policy"
                                                      class="nav-link p-0 text-white">Policies</a></li>
                         <li class="nav-item mb-2"><a href="/about/edi-products"