feat(docs): add notices for "deprecated" fields and variables

[bshaffer]

We can now add handy notices for parameters. This is done through the notice_type and notice_content fields in the DocFX YAML:

syntax:
  parameters:
  - id: data
    var_type: array
    description: description
    notice_type: deprecated
    notice_content: 'This description will be added to the deprecated note.'

This can be applied to "deprecated" fields, but could be applied to other fields in the future. We can start by adding support for deprecated fields!

See go/cloud-rad-devsite-notices