Integrate Product Analytics initialization worker with Snowplow configurator service

With https://gitlab.com/gitlab-org/analytics-section/product-analytics/devkit/-/merge_requests/48+, ~"group::product intelligence" plans to build an service within the Product Analytic stack that will handle the setup of a GitLab project to be able to collect events with Snowplow.

As illustrated below by @mwoolf, we currently employ ProductAnalytics::JitsuAuthentication to authenticate with Jitsu, establish a connection to ClickHouse, and create an assigned API key to be able to attribute events to with the aforementioned Clickhouse connection.

This issue is for any integration work that has to be done to switch the setup flow from Jitsu over to Snowplow.

Feature flag

Please add any Snowplow-specific functionality in addition to what exists for Jitsu behind the product_analytics_snowplow_support feature flag.

This is so we can coordinate a switchover with the external cluster changes and we'll remove the Jitsu-specific code when the feature flag is removed.