Implement and Measure MR by Type

## Goal
After sitting in the Cross-functional prioritization adoption AMA AMER/EMEA discussion 6/15 8:30am Pacific, I learned a lot on how product teams allocate work. [Here's that agenda doc](https://docs.google.com/document/d/13iobEuygqGi3L4Lczu72zoKuzuL_8fHmUpN7xQzZZGs/edit?usp=sharing) & [recording](https://drive.google.com/file/d/1w-4-DsUaIgbMXHF2f3rxjzxfpSa8OdvA/view?usp=sharing). 

To support [GitLab's long-term product health and stability](https://about.gitlab.com/handbook/product-development-flow/cross-functional-prioritization.html), teams are asked to plan their milestones with an appropriate mix of `type::feature`, `type::maintenance`, and `type:bug` work. MR Type labels help us report what we're working on to leadership in a way that's consistent across the engineering department.

This issue is for aligning with the Digital Experience team on these items: 

1. Introduce merge request types for the Digital Experience team to align with the [Cross Functional Prioritization](https://about.gitlab.com/handbook/product-development-flow/cross-functional-prioritization.html) process of product groups. We have some merge request types being implement as part of the approval process being worked on [here](https://gitlab.com/groups/gitlab-com/marketing/digital-experience/-/epics/135). Should we add additional types for bugs, maintenance, and features? 
1. Create a dashboard for MR by Type for Digital Experience. Dashboards listing MR by Type were created and added to every group for product as part of [this issue](https://gitlab.com/gitlab-com/www-gitlab-com/-/issues/13294). Here is the [Merge Request Types Detail periscope dashboard](https://app.periscopedata.com/app/gitlab/976854/Merge-Request-Types-Detail) for product. 
1. Update [Repository Health Days and Weeks](https://about.gitlab.com/handbook/marketing/digital-experience/#repository-health-day) with our new process

### Jobs To Be Done
* **Situation**: *Digital Experience has no way to measure MRs or what type of work it's contributing to*
* **Motivation**: *We want to implement MR types and measure them*
* **Outcome**: *So we can support GitLab's long-term product health and stability*

## Page(s)
Which page(s) are related to this request?
* https://about.gitlab.com/handbook/marketing/digital-experience/#repository-health-day
* https://about.gitlab.com/handbook/product-development-flow/cross-functional-prioritization.html
* https://about.gitlab.com/company/team/structure/working-groups/next-prioritization/
* https://gitlab.com/gitlab-com/www-gitlab-com/-/issues/13294
* https://app.periscopedata.com/app/gitlab/976854/Merge-Request-Types-Detail

## DCI
[DRI, Consulted, Informed](https://about.gitlab.com/handbook/people-group/directly-responsible-individuals/#dri-consulted-informed-dci)

- [ ] DRI: `GitLab Handle`
- [ ] Consulted: @mpreuss22 @fqureshi @justin.vetter @laurenbarker 
- [ ] Informed: `Everyone`

## In scope
What is within scope of this request?
- [ ] Implementing MR by Type
- [ ] Create Digital Experience Periscope dashboard to measure MR by Type
- [ ] Updating the Digital Experience handbook

## Requirements
What are the requirements for this request? Checklist below is an example of common requirements, please check all that apply and adjust as necessary:

- [ ] Copy writing
- [ ] Illustration
- [ ] Custom Graphics
- [x] Research
- [ ] Data / Analytics
- [ ] UX Design
- [x] Engineering

Story points: 2.0