fix(events): align V1 posting with OpenAPI

[Teko012]

What does this PR do?

Fixes pup events post and generic pup api -X POST v1/events authentication to match the Datadog V1 Events API. The create-event endpoint now accepts DD_API_KEY without requiring DD_APP_KEY, rejects unsupported bearer-only authentication before sending a request, and emits only DD-API-KEY.

The event-post command also aligns with the pinned V1 OpenAPI specification by supporting every documented request field, all seven alert types, and the documented aggregation-key, text-length, and event-age limits. Existing dogshell-compatible aliases and --handle behavior remain available.

Motivation

PR #654 added dogshell-compatible event posting, but the command inherited Pup's general authentication validation, which requires both an API key and an application key. The generated V1 create_event operation requires only apiKeyAuth, so valid API-key-only configurations were rejected before the request could be sent.

This follow-up brings both typed and raw event posting in line with the endpoint security requirement and current request schema without changing authentication for event list, search, or get operations.

Additional Notes

• API-key-only routing is limited to the exact POST /api/v1/events path.
• Generic API routing derives the auth path from the parsed URL, so query strings and fragments cannot bypass endpoint-specific requirements.
• Other OAuth-excluded endpoints continue to require both DD_API_KEY and DD_APP_KEY.
• Canonical --device-name and --source-type-name flags retain the legacy --device, --type, and underscore-style aliases.
• Blank title/message rejection, stdin normalization, local-host defaults, and --no_host behavior remain unchanged.
• The full test suite passes 1,570 tests.
• cargo clippy --tests -- -D warnings and cargo fmt --all --check pass.

Checklist

• The code change follows the project conventions (see CONTRIBUTING.md)
• Tests have been added/updated
• Documentation remains accurate
• All CI checks pass
• Code coverage is maintained or improved

Related Issues

Follow-up to #654.