Create Leads::GitlabCom::AddonsController
## Summary
Create a new `Leads::GitlabCom::AddonsController` on CustomersDot to handle addon-related lead creation for GitLab.com.
## Problem
The `trials_controller.rb#create_addon` method currently handles both lead creation and addon trial application. This needs to be separated - this issue extracts the lead creation portion into a dedicated controller.
## Implementation Details
### New Controller
**File:** `app/controllers/leads/gitlab_com/addons_controller.rb`
**Responsibilities:**
- Handle addon-related lead creation for GitLab.com users (Duo Pro, Duo Enterprise, etc.)
- Validate lead parameters
- Integrate with lead tracking systems (Marketo, Salesforce, etc.)
- Return appropriate success/error responses
### Extract from trials_controller.rb
- Lead creation logic from `create_addon` method
- Related validations for lead data
- Lead-specific error handling
- Any lead-specific helper methods
**Important:** Do NOT extract addon trial application logic - that stays in `trials_controller.rb#create_addon` until we migrate in another epic
### Routes
Add to `config/routes.rb`:
```ruby
namespace :leads do
namespace :gitlab_com do
resources :addons, only: [:create]
end
end
```
**New endpoint:** `POST /leads/gitlab_com/addons`
issue