Docs: Clarify from-to-www redirect direction. (#11692)

* docs: Clarify from-to-www redirect direction.

This was not clear to me when reading the docs whether the ingress will
redirect from non-www to with-www or the reverse. It's also not very
clear from just grepping around the codebase. I found the answer by
reading from this reddit link:

https://www.reddit.com/r/kubernetes/comments/pbl033/k8s_ingress_redirecting_www_to_nonwww_domains/

So, to save time for other people doing the same, which I assumes is a
lot of people since it's a common scenario, this little revision in the
docs is warranted.

* Docs: Implement suggestion.

---------

Co-authored-by: Chakrit Wichian <service@chakrit.net>
Co-authored-by: Marco Ebert <marco_ebert@icloud.com>

docs/user-guide/nginx-configuration/annotations.md

@@ -638,7 +638,10 @@ To preserve the trailing slash in the URI with `ssl-redirect`, set `nginx.ingres
 
 ### Redirect from/to www
 
-In some scenarios is required to redirect from `www.domain.com` to `domain.com` or vice versa.
+In some scenarios, it is required to redirect from `www.domain.com` to `domain.com` or vice versa, which way the redirect is performed depends on the configured `host` value in the Ingress object.
+
+For example, if `.spec.rules.host` is configured with a value like `www.example.com`, then this annotation will redirect to `example.com`. If `.spec.rules.host` is configured with a value like `example.com`, so without a `www`, then this annotation will redirect to `www.example.com` instead.
+
 To enable this feature use the annotation `nginx.ingress.kubernetes.io/from-to-www-redirect: "true"`
 
 !!! attention

internal/ingress/annotations/redirect/redirect.go

@@ -51,7 +51,7 @@ var redirectAnnotations = parser.Annotation{
 			Validator:     parser.ValidateBool,
 			Scope:         parser.AnnotationScopeLocation,
 			Risk:          parser.AnnotationRiskLow, // Low, as it allows just a set of options
-			Documentation: `In some scenarios is required to redirect from www.domain.com to domain.com or vice versa. To enable this feature use this annotation.`,
+			Documentation: `In some scenarios, it is required to redirect from www.domain.com to domain.com or vice versa, which way the redirect is performed depends on the configured host value in the Ingress object.`,
 		},
 		temporalRedirectAnnotation: {
 			Validator: parser.ValidateRegex(parser.URLIsValidRegex, false),