Extend Cells blueprint with Work streams, Availability and Iterations

What does this MR do and why?

Extend Cells blueprint with Work streams, Availability and Iterations

• This adds Work streams that describe Key coherent changes
• Availability what we expect at each level (Experiment, Beta and GA)
• Iterations on what we want to pick at a given iteration

Related to https://gitlab.com/gitlab-org/enablement-section/data-stores/-/issues/41