Draft: User logged in cookie

What does this MR do and why?

We would like to create a first party cookie in the product that will enable the marketing site to recognize a logged in Gitlab user.

Engineering Notes

The user's session ID can be stored in a cookie on the client-side, and sent with each request to the server. The server can then look up the user's session in the database(or API) to determine if they are logged in or not.

This solution was also suggested by a Staff Support Engineer in the #g_manage_auth slack channel

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.