docs: extensions (#1258)

* docs: process docs to include UX Stories requirement

* docs: include note regarding different environments

* Services init

* Remove unused canny logos

* docs: add ModalService diagram

* docs: GIF of notification

* docs: add ui-services page

* docs: simplify ui services call out in the general services docs

* docs: tips and tricks for UI services

* docs: moar pages

* docs: dialog gif

* docs: services in summary/sidebar

* docs: gif examples at top of dialog and notification pages

* docs: add UIModal gif

* docs: details for Dialog Service

* docs: include usage information for ui modal service

* docs: detailed information about our UI Notification Service

* docs: services diagram

* docs: remove unused links

* docs: services example and image

* docs: stubbing extension pages

* docs: UX Stories --> User Cases

* chore: eslint fix

* docs: extensions overview + diagram

* docs: update extensions in sidebar

* docs: extension skeleton and registration info

* docs: copy of maintained extensions table partial in the extensions folder

* docs: swap out old extensions structure for new

docs/latest/our-process.md

@@ -95,11 +95,11 @@ appropriate:
 | [PR: Awaiting Review 👀][awaiting-review]      | The core team has not yet performed a code review.                                                          |
 | [PR: Awaiting Revisions 🖊][awaiting-revisions] | Following code review, this label is applied until the author has made sufficient changes.                  |
 | **QA**                                         |                                                                                                             |
-| [PR: Awaiting UX Stories 💃][awaiting-stories] | The PR code changes need common language descriptions of impact to end users before the review can start    |
+| [PR: Awaiting User Cases 💃][awaiting-stories] | The PR code changes need common language descriptions of impact to end users before the review can start    |
 | [PR: No UX Impact 🙃][no-ux-impact]            | The PR code changes do not impact the user's experience                                                     |
 
 We rely on GitHub Checks and integrations with third party services to evaluate
-changes in code quality and test coverage. Tests must pass and UX stories must
+changes in code quality and test coverage. Tests must pass and User cases must
 be present (when applicable) before a PR can be merged to master, and code
 quality and test coverage must not changed by a significant margin. For some
 repositories, visual screenshot-based tests are also included, and video