Add stages and features overview

Some of the internally most often used pages are https://about.gitlab.com/handbook/product/categories/ and https://about.gitlab.com/handbook/product/categories/features/.

Data sources for these pages are:

• https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/stages.yml
• https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/features.yml
• additionally we can leverage https://about.gitlab.com/company/team/team.yml

Having an interface that let's you search by stage / group / person / feature / role for the right person to tag or chat would be very useful to find your way around inside the company.

Add an interface that facilitates that use case