feat: Accessibility improvements (#7224)

* feat: adds a11y for ContentType & Responses region

* feat: adds a11y to expandable/collapsible elements

* fix: add aria label to select element for content types

* fix: add aria label prop to contentType component

* Change optag to h3 for better tag hierarchy


Co-authored-by: ediiotero <eddie.otero@oddball.io>
Co-authored-by: Mike Lumetta <mike.lumetta@adhocteam.us>
Co-authored-by: Alexander Valencia <alex.valencia@adhocteam.us>

test/unit/components/operation-tag.jsx

@@ -44,6 +44,7 @@ describe("<OperationTag/>", function(){
 
     const opblockTag = wrapper.find(".opblock-tag")
     expect(opblockTag.length).toEqual(1)
+    expect(opblockTag.getNode().type).toEqual("h3")
 
     const renderedLink = wrapper.find("Link")
     expect(renderedLink.length).toEqual(1)