Epic: Possible CMS Offering

[apburnes]

An initial issue to track a possible future CMS offering.

### Tasks
- [ ] https://github.com/cloud-gov/pages-core/issues/4574
- [ ] https://github.com/cloud-gov/pages-core/issues/4576
- [ ] https://github.com/cloud-gov/pages-core/issues/4615
- [ ] Defining a test rubric for comparing available CMS
- [ ] https://github.com/cloud-gov/pages-core/issues/4629
- [ ] Use sample sites to identify common UI components
- [ ] Use sample sites to identify common content types
- [ ] Setup a prototype editing experience for users to test
- [ ] Outline management path to maintain layouts, components and theming.
- [ ] Putting a pitch together to possibly get TMF funds

[drewbo]

Some initial thoughts here: https://docs.google.com/document/d/1BdMIdohE35znjpy2hG5NPxGfvzIg319t1g2oMYECBl8/edit