[Analytics Unique Instance ID] Add Documentation for unique_instance_id Usage in Seat Links

Background

groupanalytics instrumentation is introducing a new unique Self-managed instance ID to be used in various instrumentation such as Service Ping and Snowplow events, as part of Introduce unique instance_id (gitlab#527150 - closed)

In order to continue correlating Self-managed instance level data using this new identifier, the Data team will need this to be added to Seat Link records as well.

This new ID will be used only for analytics while coexisting with the current instance_identifier. The instance_identifier will continue using Gitlab::CurrentSettings.uuid from the GitLab Self-managed instance database and maintain its existing functionality in CustomersDot and Cloud Connector as it does today (e.g., Cloud Connector access tokens, cloud license associations, etc.).

Proposal

Update the following documentation to include information about the unique_instance_id field and its usage within Seat Links:

• GitLab documentation
  • https://docs.gitlab.com/subscriptions/manage_subscription/
  • https://docs.gitlab.com/legal/licensing_policy/#visibility-into-latest-usage-data-and-how-to-identify-which-of-the-customers-instances-the-data-is-for
• CustomersDot documentation (if applicable)

Result

Documentation contains latest information on the unique_instance_id and its usage within Seat Links