Add Product Analytics spec for custom dashboard creation

What does this MR do and why?

Add test for Product Analytics in order to check that custom dashboard can be created an will display expected values.

The plan is to run this test in Product Analytics devkit pipelines for now as it needs Product Analytics services running and connected to Gitlab. Later it can be configured to run within gitlab-org/gitlab pipelines.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Test passing when running locally against GDK

How to set up and validate locally

Instructions on how to run Product Analytics tests against local GDK can be found here.