Create partial for <script> tags to handle dev vs production mode differences

[chalin]

• Context: Scripts tweak to cleanup whitespace etc #1262,
  https://github.com/google/docsy/pull/1262/files#r990642799
• Factor out an equivalent of the following into a script partial:

  {{ $c2cJS := resources.Get "js/click-to-copy.js" -}}
  {{ if hugo.IsProduction -}}
    {{ $c2cJS = $c2cJS | minify | fingerprint -}}
  {{ end -}}
  <script defer src="{{ $c2cJS.RelPermalink }}" {{ with $c2cJS.Data.Integrity -}}
    integrity="{{ . }}" {{ end -}}
    crossorigin="anonymous"></script>

Notes:

• For local resources, we don't need crossorigin AFAIK. In anycase, anonymous is the default. Note sure why it has been specified explicitly.
• MDN docs on crossorigin

/cc @geriom