[CHA-1427] support campaigns

[rafaelmf3]

Add Campaign Feature Support to Java SDK

Summary

This PR adds complete campaign feature support to the stream-chat-java SDK, matching the Python SDK implementation. All 7 backend campaign routes are now fully implemented and tested.

Backend Routes Implemented

• ✅ POST /campaigns - Create campaign
• ✅ GET /campaigns/{id} - Get campaign by ID
• ✅ PUT /campaigns/{id} - Update campaign
• ✅ DELETE /campaigns/{id} - Delete campaign
• ✅ POST /campaigns/{id}/start - Start campaign (with optional scheduling)
• ✅ POST /campaigns/{id}/stop - Stop campaign
• ✅ POST /campaigns/query - Query campaigns with filters and sorting

Changes

New Files

• src/main/java/io/getstream/chat/java/services/CampaignService.java - Retrofit service interface

  • All 7 campaign endpoint methods with proper Retrofit annotations
  • Follows existing service patterns (CommandService, ChannelService)

• src/main/java/io/getstream/chat/java/models/Campaign.java - Campaign model class

  • Main Campaign class with all fields (id, name, description, senderId, status, etc.)
  • Nested data structures: MessageTemplate, MemberTemplate, ChannelTemplate
  • Request data classes with @Builder pattern for all operations
  • Request classes extending StreamRequest<T> for all operations
  • Response classes extending StreamResponseObject for all operations
  • Static factory methods: create(), get(), update(), delete(), start(), stop(), query()

Test Files

• src/test/java/io/getstream/chat/java/CampaignTest.java - Comprehensive JUnit 5 tests covering:
  • Campaign creation (with and without ID)
  • Full CRUD operations
  • Start/stop with scheduling
  • Query campaigns with filters and sorting
  • Proper cleanup in all tests

Features

• Fluent API: Builder pattern for request construction
• Type Safety: Proper use of @NotNull and @Nullable annotations
• JSON Mapping: Jackson annotations for proper serialization/deserialization
• DateTime Support: Date type for scheduled_for and stop_at parameters
• Query Support: Full filter conditions, sorting, and pagination using FilterCondition and Sort utilities
• Lombok Integration: Uses @Data, @Builder, @Getter, @EqualsAndHashCode for boilerplate reduction

Code Quality

• ✅ All code follows Java SDK patterns (Command model pattern)
• ✅ Proper Lombok annotations usage
• ✅ All request/response classes properly extend base classes
• ✅ Comprehensive unit tests with proper cleanup
• ✅ No linting errors in new code
• ✅ Follows existing naming conventions and code style

Testing

All campaign tests pass successfully:

• Campaign creation (with and without ID)
• Full CRUD operations
• Start/stop with scheduling
• Query campaigns with filters
• Proper test cleanup

Example Usage

// Create a campaign

MessageTemplate messageTemplate = new MessageTemplate();
messageTemplate.setText("Hello");

Campaign campaign = Campaign.create()
    .senderId("user-1")
    .userIds(List.of("user-2"))
    .messageTemplate(messageTemplate)
    .name("My Campaign")
    .request()
    .getCampaign();

// Get a campaign

Campaign retrieved = Campaign.get(campaignId)
    .request()
    .getCampaign();

// Update a campaign

Campaign updated = Campaign.update(campaignId)
    .name("Updated Name")
    .messageTemplate(messageTemplate)
    .senderId("user-1")
    .userIds(List.of("user-2"))
    .request()
    .getCampaign();

// Start a campaign with scheduling

Calendar cal = Calendar.getInstance();
cal.add(Calendar.HOUR, 1);
Date scheduledFor = cal.getTime();

Campaign started = Campaign.start(campaignId)
    .scheduledFor(scheduledFor)
    .stopAt(stopAt)
    .request()
    .getCampaign();

// Stop a campaign

Campaign stopped = Campaign.stop(campaignId)
    .request()
    .getCampaign();

// Query campaigns

List<Campaign> campaigns = Campaign.query()
    .filter(FilterCondition.eq("id", campaignId))
    .sorts(List.of(Sort.builder()
        .field("created_at")
        .direction(Sort.Direction.DESC)
        .build()))
    .limit(10)
    .request()
    .getCampaigns();

// Delete a campaign
Campaign.delete(campaignId).request();

CLA

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request