docs: fix typos and update https references (#8154)

Co-authored-by: Tim Lai <timothy.lai@smartbear.com>

src/plugins/add-plugin.md

@@ -66,7 +66,7 @@ export function SomePlugin(toolbox) {
             getState => getState(), // This is a requirement... because we `bind` selectors, we don't want to bind to any particular state (which is an immutable value) so we bind to a function, which returns the current state
             state => state.get("something") // return the whatever "something" points to
           ),
-          foo: getState => "bar" // In the end selectors are just fuctions that we pass getState to
+          foo: getState => "bar" // In the end selectors are just functions that we pass getState to
         }
       }