docs(signals): document optional event filter for attributes [AISP-1067]

[snowplow-claude-review]

Updates the Signals attribute configuration docs to explain that the event filter is now optional: leaving it empty targets all event types rather than requiring explicit enumeration.

All changes are in docs/signals/attributes/attributes/index.md:

• Intro and "Configure the attribute" paragraph updated to reflect that events is optional.
• "Select events" section intro updated.
• Console tab gains a tip callout explaining that an empty filter matches all events.
• Python SDK tab updated with events=[] semantics and an example snippet.
• "All attribute options" table: events row updated from required to optional with a revised description.
• Two new end-to-end examples added: Global event counter (n_events_30d counter, 30-day period, events=[]) and First UTM medium across all events (first aggregation on mkt_medium, events=[]).

Reviewer: check that the new examples are syntactically valid for both Console and Python SDK tabs, and that the options table accurately reflects the updated field semantics.

---

Draft PR opened for review — please verify and run CI before merging.

[Snowplow CLA bot (snowplowcla)]

Thanks for your pull request. Is this your first contribution to a Snowplow open source project? Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://docs.snowplowanalytics.com/docs/contributing/contributor-license-agreement/ to learn more and sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

The latest updates on your project. Learn more about integrating Git with Workers.

Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	documentation	cdf259b	Commit Preview URL Branch Preview URL	Jul 27 2026, 01:34 PM