ref(uptime): Move subscription limit check to validator

[jasonyuezhang]

Move uptime subscription limit checking from exception handling in
create() to validator validation method. This ensures limits are checked
during validation phase when creating new uptime monitors, providing
consistent error responses and cleaner code.

Follows the same pattern as cron monitors for consistency.\n\n---\nCopied from getsentry#100904\nOriginal PR: getsentry#100904

[propel-test-bot]

Refactor: Move Uptime Subscription Limit Check Into Validator

This pull request refactors where organization uptime subscription limits are enforced. The check to prevent exceeding the maximum number of manual uptime monitors per organization is moved from exception handling in the create_uptime_detector function to the validation phase in the UptimeMonitorValidator. This adjustment ensures that such limits are checked earlier (during validation), yielding more consistent error responses and aligning the uptime monitor behavior with cron monitor validation patterns. Supporting utility logic is extracted into a new function, check_uptime_subscription_limit, in src/sentry/uptime/subscriptions/subscriptions.py.

Key Changes

• Added check_uptime_subscription_limit function to src/sentry/uptime/subscriptions/subscriptions.py for enforcing org-level manual monitor limits.
• Moved limit checking logic from the create_uptime_detector implementation into the validate method of UptimeMonitorValidator in src/sentry/uptime/endpoints/validators.py.
• Removed redundant checks for manual subscription limits from the create_uptime_detector function.
• Updated logic to ensure subscription limit exceptions now trigger serializers.ValidationError during validation, not in exception handling post-create.

Affected Areas

• src/sentry/uptime/endpoints/validators.py
• src/sentry/uptime/subscriptions/subscriptions.py

This summary was automatically generated by @propel-code-bot