fix: Welcome email copy changes and canned response API error handling [cw-1290] (#6905)

* fix: Welcome email copy changes and canned response API error handling

* Review fixes

* Uses mixin for alerts in canned page

* Typo fixes

* Copy changes

* Fixes broken tests

* Fixes review comments

* Fixes typo errors with mail template

* Removes unwanted case

* Fixes repetitive texts

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

spec/mailers/confirmation_instructions_spec.rb

@@ -22,7 +22,7 @@ RSpec.describe 'Confirmation Instructions', type: :mailer do
     end
 
     it 'uses the user\'s name' do
-      expect(mail.body).to match("Welcome, #{CGI.escapeHTML(confirmable_user.name)}!")
+      expect(mail.body).to match("Hi #{CGI.escapeHTML(confirmable_user.name)},")
     end
 
     it 'does not refer to the inviter and their account' do
@@ -39,7 +39,7 @@ RSpec.describe 'Confirmation Instructions', type: :mailer do
 
       it 'refers to the inviter and their account' do
         expect(mail.body).to match(
-          "#{CGI.escapeHTML(inviter_val.name)}, with #{CGI.escapeHTML(account.name)}, has invited you to try out Chatwoot!"
+          "#{CGI.escapeHTML(inviter_val.name)}, with #{CGI.escapeHTML(account.name)}, has invited you to try out Chatwoot."
         )
       end