feat(sidebar): add support for external avatar

- Add [params.sidebar.avatar] section in config.toml, with 2 fields: local and src

Migration guide:
 - Copy the old value of params.sidebar.avatar to param.sidebar.avatar.src
 - Set params.sidebar.avatar.local = true

exampleSite/config.toml

@@ -21,8 +21,10 @@ DefaultContentLanguage = "en"                   # Theme i18n support
         
     [params.sidebar]
         emoji = "🍥"
-        avatar = "img/avatar.png"
         subtitle = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."
+        [params.sidebar.avatar]
+            local = true
+            src = "img/avatar.png"
         
     [params.article]
         math = false

layouts/partials/sidebar/left.html

@@ -8,10 +8,10 @@
     <header class="site-info">
         {{ with .Site.Params.sidebar.avatar }}
             <figure class="site-avatar">
-                {{ if in (.) "http" }}
-                    <img src="{{ . }}" width="300" height="300" class="site-logo" loading="lazy" alt="Avatar">
+                {{ if not .local }}
+                    <img src="{{ .src }}" width="300" height="300" class="site-logo" loading="lazy" alt="Avatar">
                 {{ else }}
-                    {{$avatar := resources.Get (.) }}
+                    {{ $avatar := resources.Get (.src) }}
                     
                     {{ if $avatar }}
                         {{ $avatarResized := $avatar.Resize "300x" }}