feat: new style for "package" headers

[runspired]

[jenweber]

We reviewed this at the Learning Team meeting today and like the improvements to visual hierarchy on the package pages.

We spotted 2 changes needed, then this can be merged:

• Can we make this something other than an h1? We noticed that there are multiple h1s on some pages. The h1 is what will be picked up by SEO, as opposed to the page's actual content focus, and having multiple h1s causes accessibility issues. This was a preexisting issue, but with increased use of the package attribute and the changes to visuals that move us away from typical heading typography, it's a good time to fix it.
• The brown text over gray does not pass color contrast standards when we checked it on https://webaim.org/resources/contrastchecker/ Oddly enough, the browser developer tools didn't catch this, maybe because some styles come from ::after.

I also noticed that the mobile look could use some iteration, but that's not a blocker. It would be a good issue for a new contributor.

Let us know if you want any help making these adjustments!

Lastly, out of scope for this PR, but maybe helpful: when writing new docs, if ember data contributors use more specific h1s like "Overview of Something" vs "Overview", the topic will show up more easily in search engine results.

[jenweber]

P.S. Thank you for your work on this!

[MinThaMie]

Found this PR during the core-learning meeting, since we are currently working on the #710 we'll make sure this comes along in some shape or form :)

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[MinThaMie]

Will close this PR in favour of the new design, took a screenshot and will add that to the projectboard