Update StandardContext to allow for gitlab team member information

Problem

For the basic problem see &10583 (closed).

Any global property that needs to be sent with an event and normally stays consistent across events, such as user_id is currently sent via the Gitlab Standard Context. Currently it, does not have a standardized way to send the information about whether someone is a Gitlab Employee. The information could be attached to the extra object, but then it would neither be documented nor standardized.

Desired Outcome

We have a property in the StandardContext that allows for differentiating between Gitlab Employees and non-employees. This property should not be required since there are events that cannot send this information

Proposed Solution:

Add a non-required boolean property called is_gitlab_team_member to the context and update the context version for frontend and backend to enable the sending of the information. The implementation of automatic sending of the event should not be tackled in this issue but separately in Automatically indicate whether User is GitLab T... (#411276 - closed) and Allow indicating whether User is GitLab Team me... (#411277 - closed).

After the implementation the data team needs to be informed to incorporate the value in their models.

Note: The user-id from this context is pseudonymized, so it can't be associated with a specific group in the data warehouse, which otherwise would be an alternative solution here