Web IDE Blueprint

What does this MR do and why?

Add the Web IDE Blueprint retrospectively to our documentation following https://about.gitlab.com/handbook/engineering/architecture/workflow/#workflow-tldr

Workflow Item	header
Determine with your manager whether to invoke the workflow.	✅
Start writing a blueprint somewhere! Depending on whether the content can be considered SAFE or not you may want to do that in a private space first. If you don't know what content to start with you can use a template. You will find a couple of suggestions there and a markdown front matter we use for status tracking.	✅
Post a link to your blueprint with a brief description in the internal #architecture channel on Slack.	❌
Involve Architecture Evolution Coach, a Principal+ Engineer who will support you throughout the process.	✅
Open an architecture evolution blueprint merge request if you have not done it already.	✅
Work with Architecture Evolution Coach, a Product Manager, Engineering Manager, and Domain Experts to get the blueprint reviewed, refined, and merged!	❌
Assign DRIs: an Engineer, an Engineering Leader, a Product Management Leader. Those people will be responsible for the blueprint moving forward.	❌