Feature Request: Attendee opt-in/opt-out consent for sharing profile with event sponsors

## Problem description

As organizers, we sometimes receive sponsor requests for attendee information so they can follow up after events. Today, there is no explicit consent flow for attendees in ocgroups, which makes it unclear what data can be shared and creates compliance and trust concerns.

## Proposed feature

Add an attendee consent mechanism at check-in that allows each attendee to explicitly opt-in or opt-out of sharing their ocgroups profile with event sponsors. This should be presented in a clear, unobtrusive way, for example:

- A checkbox in the check-in UI: "I agree to share my ocgroups profile with sponsors of this event."
- A linked short consent notice that follows GDPR-style standards (purpose, data categories, retention, withdrawal).

## Scope and behavior

- Where this appears: In the attendee check-in flow for CNCF open community group events using ocgroups.
- Default state: Checkbox default is unchecked, so sharing only happens on explicit opt-in.
- What is shared: Attendee ocgroups profile fields already collected by the platform (e.g. name, email, company, role), configurable by maintainers.
- Who can access it: Event sponsors associated with that specific event, via an export or view limited to attendees who opted in.

## Requirements and constraints

- GDPR and privacy alignment: Consent must be explicit, informed, and easily revocable. Include a link to a privacy/consent policy that CNCF or ocgroups maintain.
- Auditability: Store a per-attendee consent flag and timestamp so organizers can demonstrate who opted in.
- Organizer workflow: Provide a way for organizers to export or view only opted-in attendees for a given event.

## Motivation

- Improves trust with attendees by making sharing transparent and opt-in instead of assumed.
- Gives sponsors a compliant way to follow up with interested attendees without manual spreadsheet hacks.
- Reduces organizer overhead by baking consent and filtering into the platform.

## Open questions

- What exact profile fields should be included by default, and should organizers be able to configure them per event?
- Should attendees be able to change their consent after check-in (e.g. via a "manage consent" link)?
- Are there CNCF standard privacy/data sharing texts that ocgroups should reference?