[BE] Multiple value streams: Deep link to selected value stream

Problem to solve

With the introduction of #221204 (closed) we will add the ability to switch value streams.

We should ensure that we also provide deep linking to the selected value stream to match the experience of the other filters on the VSA page.

This is the backend portion.

frontend work is tracked in #229489 (closed)

User experience goal

A user can return to the same configuration of filters on the Value stream analytics page by a URL. No interaction with the UI should be required.

Implementation

Make sure that ValueStream is passed to RequestParams and it's exposed through the to_data_attributes method.

File: ee/lib/gitlab/analytics/cycle_analytics/request_params.rb

Links / references

Similar to: #32426 (closed)