docs: Fix RFC 1123 label names documentation

Correct RFC 1123 label names to require starting with alphabetic character
to match the actual Kubernetes implementation regex [a-zA-Z]([-a-zA-Z0-9]*[a-zA-Z0-9])?.

Add note about RelaxedServiceNameValidation feature gate exception for Services.

Update explanation of RFC differences to reflect actual implementation where
both RFC 1035 and RFC 1123 require starting with alphabetic characters,
with the exception being the RelaxedServiceNameValidation feature gate for
Service objects.

This addresses issue 52578.

Signed-off-by: srikanth-s2003 <[email protected]>

Author: srikanth-s2003

content/en/docs/concepts/overview/working-with-objects/names.md

@@ -59,9 +59,14 @@ This means the name must:
 
 - contain at most 63 characters
 - contain only lowercase alphanumeric characters or '-'
-- start with an alphanumeric character
+- start with an alphabetic character
 - end with an alphanumeric character
 
+{{< note >}}
+When the `RelaxedServiceNameValidation` feature gate is enabled,
+Service object names are allowed to start with a digit.
+{{< /note >}}
+
 ### RFC 1035 Label Names
 
 Some resource types require their names to follow the DNS
@@ -74,10 +79,10 @@ This means the name must:
 - end with an alphanumeric character
 
 {{< note >}}
-The only difference between the RFC 1035 and RFC 1123
-label standards is that RFC 1123 labels are allowed to
-start with a digit, whereas RFC 1035 labels can start
-with a lowercase alphabetic character only.
+While RFC 1123 technically allows labels to start with digits, the current
+Kubernetes implementation requires both RFC 1035 and RFC 1123 labels to start
+with an alphabetic character. The exception is when the `RelaxedServiceNameValidation`
+feature gate is enabled for Service objects, which allows Service names to start with digits.
 {{< /note >}}
 
 ### Path Segment Names