chore: add sidekiq_alive gem for health check endpoint (#12008)

```
➜  chatwoot git:(feat/sidekiq-health) curl -I localhost:7433
HTTP/1.1 200 OK
Server: SidekiqAlive/2.5.0 (Ruby/3.4.4)
Connection: Keep-Alive
Date: Tue, 22 Jul 2025 10:34:28 GMT
Content-Length: 6

➜  chatwoot git:(feat/sidekiq-health) curl localhost:7433
Alive!%
```

fixes: https://github.com/chatwoot/chatwoot/issues/10948

Gemfile

@@ -121,6 +121,8 @@ gem 'sentry-sidekiq', '>= 5.19.0', require: false
 gem 'sidekiq', '>= 7.3.1'
 # We want cron jobs
 gem 'sidekiq-cron', '>= 1.12.0'
+# for sidekiq healthcheck
+gem 'sidekiq_alive'
 
 ##-- Push notification service --##
 gem 'fcm'

Gemfile.lock

@@ -359,6 +359,7 @@ GEM
     grpc (1.72.0-x86_64-linux)
       google-protobuf (>= 3.25, < 5.0)
       googleapis-common-protos-types (~> 1.0)
+    gserver (0.0.1)
     haikunator (1.1.1)
     hairtrigger (1.0.0)
       activerecord (>= 6.0, < 8)
@@ -785,6 +786,9 @@ GEM
       fugit (~> 1.8)
       globalid (>= 1.0.1)
       sidekiq (>= 6)
+    sidekiq_alive (2.5.0)
+      gserver (~> 0.0.1)
+      sidekiq (>= 5, < 9)
     signet (0.17.0)
       addressable (~> 2.8)
       faraday (>= 0.17.5, < 3.a)
@@ -1010,6 +1014,7 @@ DEPENDENCIES
   shoulda-matchers
   sidekiq (>= 7.3.1)
   sidekiq-cron (>= 1.12.0)
+  sidekiq_alive
   simplecov (= 0.17.1)
   slack-ruby-client (~> 2.5.2)
   spring