Fall back to Hugo's default behavior for disableHugoGeneratorInject

[chalin]

• Fixes Docsy does not respect configuration parameter "disableHugoGeneratorInject" #1707
  That is, without this PR we get the generator meta tag in every page:

  $ find userguide/public/* -type f -name "*.html" -exec grep -nH -e 'name="generator"' {} +
  userguide/public/404.html:6:<meta name="generator" content="Hugo 0.120.4">
  userguide/public/about/index.html:6:<meta name="generator" content="Hugo 0.120.4">
  userguide/public/blog/2022/hello/index.html:6:<meta name="generator" content="Hugo 0.120.4">
  ...

• With this fix, with or without disableHugoGeneratorInject set to true, we get the Hugo-default behavior of at most adding the meta tag to the homepage:

  $ npm run build 
  $ find userguide/public/* -type f -name "*.html" -exec grep -nH -e 'name="generator"' {} +
  userguide/public/index.html:4:  <meta name="generator" content="Hugo 0.120.4">
  $ HUGO_DISABLEHUGOGENERATORINJECT=true npm run build                                                
  $ find userguide/public/* -type f -name "*.html" -exec grep -nH -e 'name="generator"' {} +
  $ 

[fekete-robert]

Works as expected