fix: Show version number with card loading spinner (#1825)

- Closes #1818

**Why add this?**: A repeated pattern is that an issue is fixed in the
card, a new build is released and users will incorrectly believe it's
not yet fixed due to their browser caching the old code. This results in
wasting their time, and my time.

**But it's obnoxious!**: I'm pretty sensitive to this (hence adding
these messages!), so let me know how terrible you find it. You can
disable it with:

```yaml
performance:
  features:
    card_loading_indicator: false
```

src/scss/themes/base.scss

@@ -124,4 +124,13 @@
 
   --frigate-card-timeline-divider-color: var(--frigate-card-divider-color);
   --frigate-card-timeline-target-bar-color: var(--frigate-card-active-color);
+
+  /*******************
+   * Loading Indicator
+   *******************/
+
+  --frigate-card-loading-background-color: var(
+    --frigate-card-control-background-transparent
+  );
+  --frigate-card-loading-foreground-color: var(--frigate-card-control-foreground);
 }