feat: Add support for image files in Captain (#11730)

# Pull Request Template

## Linear links:
-
https://linear.app/chatwoot/issue/CW-4479/if-image-is-sent-by-the-customer-send-it-to-openai

## Description

This pull request adds “Captain image support” to Chatwoot. It
introduces multimodal message handling so that when a customer sends an
image, Captain can forward the file to OpenAI’s vision endpoint,
generate a caption/analysis
## Type of change

Please delete options that are not relevant.

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

<img width="891" alt="image"
src="https://github.com/user-attachments/assets/c7cc98ed-cc44-4865-a53a-83d129e2fe2c"
/>



## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Pranav <pranav@chatwoot.com>

spec/enterprise/controllers/api/v1/accounts/captain/assistants_controller_spec.rb

@@ -211,8 +211,8 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
 
         expect(response).to have_http_status(:success)
         expect(chat_service).to have_received(:generate_response).with(
-          valid_params[:message_content],
-          valid_params[:message_history]
+          additional_message: valid_params[:message_content],
+          message_history: valid_params[:message_history]
         )
         expect(json_response[:content]).to eq('Assistant response')
       end
@@ -232,8 +232,8 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
 
         expect(response).to have_http_status(:success)
         expect(chat_service).to have_received(:generate_response).with(
-          params_without_history[:message_content],
-          []
+          additional_message: params_without_history[:message_content],
+          message_history: []
         )
       end
     end