Add Google Analytics 4 to the Velero website (#10583)

Adds a gtag.js partial wired into both site head templates (baseof.html and
head-docs.html) so every page on velero.io reports into a single GA4 property.

The Measurement ID (G-XX7MWLVX37) is a CNCF-provisioned property for the Velero
project (CNCF Service Desk CNCFSD-3824). The tag renders only in production
builds, so local development and Netlify PR previews are excluded from the data.

This also satisfies the CLOMonitor analytics check for our CNCF incubation
work.

Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>

site/config.yaml

@@ -7,6 +7,7 @@ frontmatter:
   date: [":filename", ":default"]
 params:
   author: Velero Authors
+  googleAnalytics: G-XX7MWLVX37
   logo: Velero.svg
   cncf_logo: cncf-color.svg
   hero:

site/layouts/_default/baseof.html

@@ -10,6 +10,7 @@
   {{ $styles := resources.Get "styles.scss" | toCSS $options | resources.Fingerprint }}
   <link rel="stylesheet" href="{{ $styles.RelPermalink }}" integrity="{{ $styles.Data.Integrity }}">
   {{ block "siteTitle" . }}<title>{{ .Site.Title }} {{ .Page.Title }}</title>{{ end }}
+  {{ partial "google-analytics.html" . }}
 </head>
 <body id="{{ .CurrentSection.Params.id }}">
 <div class="container-fluid site-outer-container">

site/layouts/partials/google-analytics.html

@@ -0,0 +1,19 @@
+{{/*
+  Google Analytics 4 (gtag.js).
+
+  Renders only in production builds (Netlify runs `hugo` with the production
+  environment, so local `hugo server` and PR previews stay out of the data).
+  The Measurement ID is read from `params.googleAnalytics` in config.yaml.
+*/}}
+{{ if hugo.IsProduction }}
+{{ with .Site.Params.googleAnalytics }}
+<!-- Google tag (gtag.js) -->
+<script async src="https://www.googletagmanager.com/gtag/js?id={{ . }}"></script>
+<script>
+  window.dataLayer = window.dataLayer || [];
+  function gtag(){dataLayer.push(arguments);}
+  gtag('js', new Date());
+  gtag('config', '{{ . }}');
+</script>
+{{ end }}
+{{ end }}

site/layouts/partials/head-docs.html

@@ -8,4 +8,5 @@
   {{ $styles := resources.Get "styles.scss" | toCSS $options | resources.Fingerprint }}
   <link rel="stylesheet" href="{{ $styles.RelPermalink }}" integrity="{{ $styles.Data.Integrity }}">
   {{/* TODO  {% seo %}*/}}
+  {{ partial "google-analytics.html" . }}
 </head>