Load citation JS only when needed (#29855)

Previously, the citation js would load every time when opening a citable
repo. Now it only loads when the user clicks the button for it. The
loading state is representend with a spinner on the button:

<img width="83" alt="Screenshot 2024-03-17 at 00 25 13"
src="https://github.com/go-gitea/gitea/assets/115237/29649089-13f3-4974-ab81-e12c0f8e651f">

Diff ist best viewed with whitespace hidden.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

web_src/css/modules/animations.css

@@ -13,6 +13,10 @@
   opacity: 0.3;
 }
 
+.button.is-loading > * {
+  opacity: 0;
+}
+
 .is-loading::after {
   content: "";
   position: absolute;

web_src/js/features/citation.js

@@ -40,28 +40,35 @@ export async function initCitationFileCopyContent() {
     $citationCopyApa.toggleClass('primary', !isBibtex);
   };
 
-  try {
-    await initInputCitationValue($citationCopyApa, $citationCopyBibtex);
-  } catch (e) {
-    console.error(`initCitationFileCopyContent error: ${e}`, e);
-    return;
-  }
-  updateUi();
+  $('#cite-repo-button').on('click', async (e) => {
+    const dropdownBtn = e.target.closest('.ui.dropdown.button');
+    dropdownBtn.classList.add('is-loading');
 
-  $citationCopyApa.on('click', () => {
-    localStorage.setItem('citation-copy-format', 'apa');
-    updateUi();
-  });
-  $citationCopyBibtex.on('click', () => {
-    localStorage.setItem('citation-copy-format', 'bibtex');
-    updateUi();
-  });
+    try {
+      try {
+        await initInputCitationValue($citationCopyApa, $citationCopyBibtex);
+      } catch (e) {
+        console.error(`initCitationFileCopyContent error: ${e}`, e);
+        return;
+      }
+      updateUi();
 
-  $inputContent.on('click', () => {
-    $inputContent.trigger('select');
-  });
+      $citationCopyApa.on('click', () => {
+        localStorage.setItem('citation-copy-format', 'apa');
+        updateUi();
+      });
+      $citationCopyBibtex.on('click', () => {
+        localStorage.setItem('citation-copy-format', 'bibtex');
+        updateUi();
+      });
+
+      $inputContent.on('click', () => {
+        $inputContent.trigger('select');
+      });
+    } finally {
+      dropdownBtn.classList.remove('is-loading');
+    }
 
-  $('#cite-repo-button').on('click', () => {
     $('#cite-repo-modal').modal('show');
   });
 }