Introduce product type markers to applies blocks/metadata

[Mpdreamz]

applies:
 cloud: ga
 self: beta

is analogous to:

applies:
  hosted: ga
  serverless: ga
  stack: beta
  eck: beta
  ece: beta

products can always overwrite a product's type availability:

applies:
  cloud: ga
  serverless: preview

I think we can also use this clean up the page level admonitions #95 so that we can limit the amount of badges a page header has if all products under a deployment type have the same product availability.