📖: Add v2 webhook implementation to multiversion tutorial

The multiversion tutorial webhooks.md was only showing the v1 webhook
implementation but not the v2 webhook implementation. This caused
confusion as the v2 webhook has different validation logic to handle
the structured CronSchedule type instead of a simple string.

Updated webhooks.md to show both:
- v1 webhook: handles conversion and validates string-based schedule
- v2 webhook: validates structured CronSchedule by building cron expression from fields

Co-authored-by: camilamacedo86 <[email protected]>

Author: Copilot

docs/book/src/multiversion-tutorial/webhooks.md

@@ -3,10 +3,21 @@
 Our conversion is in place, so all that's left is to tell
 controller-runtime about our conversion.
 
-## Webhook setup...
+## Webhook setup for v1...
+
+The v1 webhook handles conversion (as the hub) and provides validation/defaulting
+for the v1 CronJob format with a string-based schedule:
 
 {{#literatego ./testdata/project/internal/webhook/v1/cronjob_webhook.go}}
 
+## Webhook setup for v2...
+
+The v2 webhook provides validation and defaulting for the v2 CronJob format
+with the structured CronSchedule type. Note how the validation logic differs
+from v1 - it builds a cron expression from the individual schedule fields:
+
+{{#literatego ./testdata/project/internal/webhook/v2/cronjob_webhook.go}}
+
 ## ...and `main.go`
 
 Similarly, our existing main file is sufficient: