feat(sms): add generic SMS alert channel with HTTP POST support

- Introduced a new SMS alert channel that allows sending notifications via any SMS API.
- The channel supports configuration through environment variables or directly in the details.
- Added validation for required fields such as api_url and recipients.
- Implemented message truncation to comply with SMS character limits.
- Updated tests to cover the new SMS channel functionality and ensure proper validation and sending behavior.
- Removed deprecated alert channels including Slack, Telegram, Teams, PagerDuty, and others from the codebase.

Author: halilibrahimd27