Create a tool for establishing customer tier/size from namespaces ids

When an incident happens we need better ways to understand its severity. A tool to gather namespaces plans and number of seats by ids could help to build a better action plan.

The initial idea was to have a rake task that could accept namespaces_ids in CSV format and output its result. A draft can be found at: !77059 (closed)

After some discussion we realized that we need to put a little bit more thinking about it, especially about what kind of information we want to output from the tool.

This is part of https://gitlab.com/gitlab-org/plan/-/issues/492 work plan.