Move web monetization link into a meta tag within the head tag

[SeanKilleen]

#710 didn't quite do what I needed it to do; I read the directions wrong.

We need this meta tag to be in the header, so we'll probably have to pull and override another include.

I suggest:

• Create an include for the meta tag, e.g. web_monetization
• Customize the include that pulls in the head tags to also include the web_monetization include
• Double-check the preview site in the browser with Coil enabled.