fix: migrate from deprecated annotate gem to annotaterb (#12845)

## Description

The `annotate` gem has been deprecated and users are experiencing
annotation errors with the new Rails 7 `serialize` syntax. This PR
migrates to `annotaterb`, the actively maintained fork.

Users reported errors when running `make db`:
```
Unable to annotate app/models/installation_config.rb: no implicit conversion of Hash into String  
Unable to annotate app/models/installation_config.rb: no implicit conversion of nil into Array
```

This PR updates the Gemfile and rake configuration to use `annotaterb`
instead.

Fixes #11673

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

Tested locally with the following steps:
1. Run `bundle install` - successfully installed annotaterb 4.20.0
2. Run `RAILS_ENV=development bundle exec rails db:chatwoot_prepare` -
completed without annotation errors
3. Run `RAILS_ENV=development bundle exec rails annotate_rb:models` -
successfully annotated all models including InstallationConfig
4. Verified InstallationConfig model annotations are present and correct

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] My changes generate no new warnings
- [x] New and existing unit tests pass locally with my changes

Gemfile.lock

@@ -128,9 +128,9 @@ GEM
       selectize-rails (~> 0.6)
     ai-agents (0.4.3)
       ruby_llm (~> 1.3)
-    annotate (3.2.0)
-      activerecord (>= 3.2, < 8.0)
-      rake (>= 10.4, < 14.0)
+    annotaterb (4.20.0)
+      activerecord (>= 6.0.0)
+      activesupport (>= 6.0.0)
     ast (2.4.3)
     attr_extras (7.1.0)
     audited (5.4.1)
@@ -992,7 +992,7 @@ DEPENDENCIES
   administrate-field-active_storage (>= 1.0.3)
   administrate-field-belongs_to_search (>= 0.9.0)
   ai-agents (>= 0.4.3)
-  annotate
+  annotaterb
   attr_extras
   audited (~> 5.4, >= 5.4.1)
   aws-sdk-s3