chore: Refactor UTM params to stay compliant with standards (#12312)

We were using UTM params on various branding urls which weren't
compliant to standard utm params and hence were ignored by analytics
tooling. this PR ensures that the params stays compliant with defined
standard

ref: https://en.wikipedia.org/wiki/UTM_parameters

## Changes 

- updated utm tags on widget and survey urls
- added utm on helpcenter branding

---------

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

spec/helpers/portal_helper_spec.rb

@@ -291,4 +291,40 @@ describe PortalHelper do
       end
     end
   end
+
+  describe '#generate_portal_brand_url' do
+    it 'builds URL with UTM params and referer host as source (happy path)' do
+      result = helper.generate_portal_brand_url('https://brand.example.com', 'https://app.chatwoot.com/some/page')
+      uri = URI.parse(result)
+      params = Rack::Utils.parse_query(uri.query)
+      expect(uri.scheme).to eq('https')
+      expect(uri.host).to eq('brand.example.com')
+      expect(params['utm_medium']).to eq('helpcenter')
+      expect(params['utm_campaign']).to eq('branding')
+      expect(params['utm_source']).to eq('app.chatwoot.com')
+    end
+
+    it 'returns utm string when brand_url is nil or empty' do
+      expect(helper.generate_portal_brand_url(nil,
+                                              'https://app.chatwoot.com')).to eq(
+                                                '?utm_campaign=branding&utm_medium=helpcenter&utm_source=app.chatwoot.com'
+                                              )
+      expect(helper.generate_portal_brand_url('',
+                                              'https://app.chatwoot.com')).to eq(
+                                                '?utm_campaign=branding&utm_medium=helpcenter&utm_source=app.chatwoot.com'
+                                              )
+    end
+
+    it 'omits utm_source when referer is nil or invalid' do
+      r1 = helper.generate_portal_brand_url('https://brand.example.com', nil)
+      p1 = Rack::Utils.parse_query(URI.parse(r1).query)
+      expect(p1.key?('utm_source')).to be(false)
+
+      r2 = helper.generate_portal_brand_url('https://brand.example.com', '::not-a-valid-url')
+      p2 = Rack::Utils.parse_query(URI.parse(r2).query)
+      expect(p2.key?('utm_source')).to be(false)
+      expect(p2['utm_medium']).to eq('helpcenter')
+      expect(p2['utm_campaign']).to eq('branding')
+    end
+  end
 end