Features page: Sticky DevOps stage headers, to discover feature-to-stage assignment faster

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#### Briefly describe the request


The names of our DevOps stages It would sticky while scrolling over that stage's features

For example:  `Manage` should remain visible while scrolling over the feature subsections `Users`, `DevOps Reports` and `Value Stream Management` (each a `<h4 class="text-left"`), or when jumping through all `LDAP` mentions with Ctrl+F.

#### What is/are the relevant URL(s)

https://about.gitlab.com/features/

#### What team/dept/company initiatives does this relate to?

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#### Is there a due date? If so, why?

No.

#### What problem(s) are we trying to solve? What are the goals?

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The lifecycle stage headings on [/features](https://about.gitlab.com/features/) (`<a class="item-link" ... <h2>` plus maybe `<p class="subhead"> ...`) can be a long distance apart from where one views the page. This necessitates a lot of scrolling up (often too far, therefore down again) to find the stage name.

#### Who is the audience?

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* GitLab employees looking up the feature-to-stage assignment, for example to then find out a DRI, stable support counterpart or technical writer on [/company/team/org-chart](https://about.gitlab.com/company/team/org-chart/) or [/handbook/product/categories](https://about.gitlab.com/handbook/product/categories/#devops-stages).

#### What are the measurable key performance indicators (KPI)?

See examples in `checklist of deliverables` below.

#### Please identify the directly responsible individual (DRI), stakeholders, and roles

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#### What are the project must-haves?

The `<h2>` stage header must remain in view while scrolling.

#### What are the project should-haves?

Maybe pinned to the to the top of its respective `<div class="features-description`, below `<header class="navbar"`.

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#### What are the project could-haves?

Instead of pin to top, maybe to the side, tilted by 90˚?

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#### Where do you expect traffic to come from?

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#### Please provide any related media files

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#### Please create a checklist of deliverables in this phase

- [ ] Update page
- [ ] Approved review of changes
- [ ] Implement AB test (for example: compare clickthrough rate for `/stages-devops-lifecycle/...` pages vs. each stage's features' docu pages)
- [ ] Release
- [ ] Evaluate results (for example: higher clickthrough rate to `/stages-devops-lifecycle/...` page due to higher/longer visibility of each stage's header)
- [ ] Code cleanup

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Story points: 2.0