templates: add aria-label attributes to interactive elements

From a11y report (and others similar)

Error: This element has role of "button" but does not have a name available to an accessibility API. Valid names are: element content, aria-label undefined, aria-labelledby undefined. WCAG2AA.Principle4.Guideline4_1.4_1_2.H91.A.Name

templates/navbar.tmpl

@@ -38,16 +38,17 @@
     <ul class="navbar-nav">
       <li class="nav-item dropdown">
         <a href="#" class="nav-link dropdown-toggle" role="button" data-bs-toggle="dropdown"
-           aria-expanded="false" id="searchDropdownMenuLink">
+           aria-expanded="false" aria-label="Search" id="searchDropdownMenuLink">
           <span class="oi oi-magnifying-glass"></span>
         </a>
         <div class="dropdown-menu" aria-labelledby="searchDropdownMenuLink">
           <form id="searchForm" class="form-inline" action="/search" role="search">
             <div class="input-group">
               <input name="q" type="text" class="form-control typeahead ai-search-box"
-                     autocomplete="off" placeholder="Search">
+                     autocomplete="off" placeholder="Search" aria-label="Search">
               <span class="input-group-btn">
-                <button id="searchBtn" type="submit" class="btn btn-default ai-search-button">
+                <button id="searchBtn" type="submit" aria-label="Submit"
+                     class="btn btn-default ai-search-button">
                   <span class="oi oi-magnifying-glass"></span>
                 </button>
               </span>
@@ -58,7 +59,8 @@
 
       <li class="nav-item dropdown">
         <a href="#" class="nav-link dropdown-toggle" data-bs-toggle="dropdown"
-           aria-haspopup="true" aria-expanded="false" id="langDropdownMenuLink">
+           aria-haspopup="true" aria-expanded="false" id="langDropdownMenuLink"
+           aria-label="Language">
           <span class="oi oi-globe"></span>
         </a>
         <ul class="dropdown-menu" aria-labelledby="langDropdownMenuLink">