[EPIC] Multiple Group IDS for the user event.

[bingzhang]

Description

To support multiple groups for a user event, also the concept of ``sub-group'' of a user event.
The main reason for this is to address the complexity that comes with splitting related data across services, which in this case is unnecessary. Essentially, the Groups BB should be viewed as a dependency of the Events BB so the Events BB will be responsible for managing all events data/features without the need for the Groups BB to be aware of events at all.

• [FEATURE] Add groupIds and userIds two fields in events bb yml file #1017
• [TASK] generate user core access token #1019
• [Feature] Support multiple groups in post endpoint. #1020
• [Feature] supports multiple group ids in the put endpoint. #1026
• [FEATURE] Support multiple Group IDs in the DELETE endpoint #1118

Acceptance Criteria

Multiple groups supported by POST, PUT, PATCH, and DELETE endpoints.

[sandeep-ps]

Please provide a description, acceptance criteria, and individual features in the epic. Thanks.