Add support for snowplow PA configurator

What does this MR do and why?

Overview

• Adds changes required to replace Jitsu with our in-house configurator and snowplow for event ingestion in groupproduct analytics.

Database changes

• Adds new application setting product_analytics_configurator_base_uri to store the base URI for the configurator service.
• Adds a new project_setting field product_analytics_instrumentation_key to store the instrumentation key.

Backend changes

• Adds a new feature flag to switch between the existing Jitsu-based stack, and the new snowplow one. This is off by default.
• Adds a new background worker to setup a stack using the new configurator.
• Adds all required specs.

Reproduction steps

• Enable the feature flag: Feature.enable(:product_analytics_snowplow_support)
• Ensure that you are running the groupproduct analytics devkit using snowplow. Instructions can be found here: https://gitlab.com/gitlab-org/analytics-section/product-analytics/devkit#snowplow-instead-of-jitsu-work-in-progress
• As an instance admin, go to Admin -> Settings -> Product Analytics and enter the configurator URL. By default this will be http://test:test@localhost:4567.
  • If you haven't used the product analytics features in the past, you'll need to enter some values in to the other fields to pass validation. We'll be removing those with the flag removal shortly.
• In a project where you are a maintainer or above, execute the ProjectInitializeProductAnalytics GraphQL mutation.
• Assert that a background job is triggered of class ProductAnalytics::InitializeSnowplowProductAnalyticsWorker and not ProductAnalytics::InitializeAnalyticsWorker.
• Assert that the value of project.project_setting.product_analytics_instrumentation_key has been correct filled.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots

• I have evaluated the MR acceptance checklist for this MR.

Related to #398253 (closed)