Create notification bar component

[alexgibson]

The upcoming Trailhead designs show a new notification both on /thanks and on /whatsnew

It also appears in our new brand guidelines:

Things to note:

• There are a range of new colors here that are not currently in our tokens.
• The bar seems like it needs to support an optional button to close the notification.

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Estimates
Eng	5

[ejregithub]

@amychurchwell - please size this work, apply the Estimate and tag it with the Priority, P1, P2, P3 assigned by Justin.

[amychurchwell]

@hoosteeno what priority would we give this task? I was considering it P2(?) because it is a piece of the work in mozilla/bedrock#7468 which is marked as P1

[hoosteeno]

This is P1. I can't seem to add labels here.

[craigcook]

Since it ties to WNP69 I think it inherits the P1 from that epic.