Add parent relationship to deprecations to allow grouping in the UI, especially in the index

[kategengler]

• Added since to the metadata display since I felt it was missing especially on the id route
• Made id in the metadata display link to the individual id page to expose those URLs
• Added some info to the README about the new relationship but also about adding deprecation guides

No deprecations currently use this, though I did certainly test it out. I am aiming to use this for #1381 so we do not lose the usefulness of the index. Due to the way the Deprecateimport Ember from 'ember'`` deprecation is done, we need a URL for every single API even if they weren't ones that were at all used by the public. I don't want the index to scare people off of upgrading to 6.0, but there should still be a way to see all the related deprecations.

cc @NullVoxPopuli

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[MinThaMie]

We discussed this during our learning meeting on 17th of June, and while we understand that it's a ton of deprecations we believe introducing this new data pattern/structure is not necessary and makes it more complicated to maintain.

We have plans to structurally address the issue you ran into. I hope you understand :) Thanks for the PoC!

[kategengler]

Do you have a timeline for addressing the issue? We're attempting to land the deprecation of import Ember from 'ember' which is the one that introduces 150 deprecations, most of which will not be relevant for most users.

[MinThaMie]

We're happy to land that deprecation as is :) it does not seem to effect the usability of the page, so you could merge import Ember from ember right now if you want to.

[kategengler]

To me it greatly affects the usability of that page. I find users often browse deprecations by version to get an idea of what is required for a particular upgrade. Adding 150 deprecations, most of which are for things that are somewhat esoteric, is very discouraging for someone looking at that list -- it isn't easy to tell at a glance that they are grouped under this deprecation of the import of Ember. It also drowns out the other deprecations with that version.