[New sample] Open Chrome API reference page (omnibox, alarms, messaging sample)

[AmySteam]

User Story

As a web developer, I want to open extension API reference pages on Chrome, so that I can quickly learn how to use a specific extension API.

Bonus: A daily extension tip will be displayed as a popover after clicking the "tip" navigation list item. (Currently, it requires Canary build and the "Experimental Web Platform features" flag enabled. The release date was moved to M114, so this approach may need to be abandoned if we want to launch before then.)

How to use it?

1. Enter the keyword "api" in the browser address bar.
2. Then, press "tab" or "space".
3. Start typing they API keyword.
4. A list the most common APIs will show or a list of past searches
5. Select the API desired, and a new page will open to the Chrome API reference page.

TODO:

• [ ] The Popover API is currently being developed. If it's not ready by the launch, then we will make adjustments. The popover was chosen to simplify the example.
• [ ] The ReadME.md will have a link to the tutorial

[AmySteam]

@sebastianbenz Thanks for the review. I applied most of your suggestions. I wrote comments on the suggestions I had a few thoughts on.

[jpmedley]

@AmySteam, later today adding a 'latest samples' entry to 'What's new'. It would be cool to include this, but I don't know how much more work you have.