fix: added prefix input validation to solution (#329)

* fix: added prefix validation

* fix: prefix validation update

* fix: prefix validation

* fix: better regex

* fix: wrong prefix length

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Co-authored-by: Akash Kumar <Ak-sky@users.noreply.github.com>

Author: kierramarie

solutions/standard/variables.tf

@@ -45,6 +45,15 @@ variable "prefix" {
   type        = string
   description = "(Optional) Prefix to add to all resources created by this solution. To not use any prefix value, you can set this value to `null` or an empty string."
   default     = "dev"
+  validation {
+    condition = (var.prefix == null ? true :
+      alltrue([
+        can(regex("^[a-z]{0,1}[-a-z0-9]{0,14}[a-z0-9]{0,1}$", var.prefix)),
+        length(regexall("^.*--.*", var.prefix)) == 0
+      ])
+    )
+    error_message = "Prefix must begin with a lowercase letter, contain only lowercase letters, numbers, and - characters. Prefixes must end with a lowercase letter or number and be 16 or fewer characters."
+  }
 }
 
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