Adds survey banner to the docs site

[cgranleese-r7]

This PR adds a user engagement survey banner. The banner will link the user to the survey. The banner can also be closed and remain closed if the user decides to do so. I have added some logic to push the site content down when the banner is present and then reverts to the original once the banner is closed.

Banner present

Banner closed

Verification

• Boot the site locally following these steps: https://github.com/rapid7/metasploit-framework/tree/master/docs#setup
• Verify the banner is present and links to the survey as expected
• Verify the banner can be closed and remain closed after refreshes and navigating to other paths
• Verify it works on mobile sized devices (use inspect then device sizes button)

[adfoster-r7]

Not a blocker, the header shouldn't contain visual elements:

The element is a container for metadata (data about data) and is placed between the tag and the tag.
Metadata is data about the HTML document. Metadata is not displayed.
Metadata typically define the document title, character set, styles, scripts, and other meta information.
https://www.w3schools.com/tags/tag_head.asp

The tag defines the document's body.
The element contains all the contents of an HTML document, such as headings, paragraphs, images, hyperlinks, tables, lists, etc.
https://www.w3schools.com/tags/tag_body.asp

I wonder if there's an alterantive place to add this so it honors HTML semantics