MSG-200: Add rcs/outbound API

[sgudimetta]

Background information

This is part of the MSG-200 ticket to add RCS (Rich Communication Services) Outbound API from the golang internal version of the infobip API to the Java client (Public Repo). This feature enables sending rich media messages including cards, carousels, and interactive suggested actions via RCS.

Implementation summary

• Created RcsApi class with sendRcsOutboundMessage method
• Created model classes: RcsOutboundRequest, RcsOutboundResponse, RcsContent, RcsCard, RcsSuggestedAction, and RcsMessageInfo
• Implemented support for text messages, rich cards, carousels, and location-based actions
• Added comprehensive JavaDoc documentation
• Applied Palantir Java Format code standards

Risk mitigation

• Added comprehensive JUnit tests with WireMock for API functionality
• Tested all content types: plain text, rich cards, carousels, and suggested actions
• Validated complex nested object serialization
• Covered error handling and edge cases
• Ensured backward compatibility with existing API structure