TW-4852 Add outbound rule support to nylas agent rule commands

[qasim-nylas]

Summary

• add outbound rule support to nylas agent rule create/update flows while keeping the existing agent-policy command surface
• introduce trigger-aware rule validation plus clearer CLI error mapping when the backend has not rolled out outbound rules yet
• update docs, demo/mock adapters, and automated coverage for outbound rule behavior

What changed

• added dedicated rule validation for inbound vs outbound triggers, including outbound-specific field checks, action constraints, and payload normalization
• wired outbound support through CLI payload building and create/update/delete flows
• fixed rule deletion guardrails so inbound-only assumptions do not incorrectly block outbound rule deletion
• surfaced the rule trigger in CLI output to make inbound vs outbound rules easier to distinguish
• refreshed command docs and examples for outbound rules
• updated demo/mock rule fixtures and added outbound-focused unit and integration tests

Rollout note

• some API environments still reject trigger=outbound
• the CLI now converts that backend response into a clearer unsupported/rollout message instead of a generic API failure
• the outbound integration test treats that backend state as unsupported and skips instead of failing the suite

Testing

• make ci-full
• outbound lifecycle integration is covered, with skip behavior in environments where the backend rollout is not enabled yet

Jira

• TW-4852
• related CLI rule-management workstream: TT-4413