fix: "wa_source_id" function return value (#5451)

- Fix contact inbox builder returning invalid WhatsApp source id
- Add specs to cover source id validations

Co-authored-by: Sojan Jose <sojan@pepalo.com>

lib/regex_helper.rb

@@ -6,4 +6,8 @@ module RegexHelper
   # shouldn't start with a underscore or hyphen
   UNICODE_CHARACTER_NUMBER_HYPHEN_UNDERSCORE = Regexp.new('\A[\p{L}\p{N}]+[\p{L}\p{N}_-]+\Z')
   MENTION_REGEX = Regexp.new('\[(@[\w_. ]+)\]\(mention://(?:user|team)/\d+/(.*?)+\)')
+
+  TWILIO_CHANNEL_SMS_REGEX = Regexp.new('^\+\d{1,14}\z')
+  TWILIO_CHANNEL_WHATSAPP_REGEX = Regexp.new('^whatsapp:\+\d{1,14}\z')
+  WHATSAPP_CHANNEL_REGEX = Regexp.new('^\d{1,14}\z')
 end