Webcrawler: Support indexing of Open Graph fields

[ComLock]

Some typical Open Graph fields:

<meta property="og:title" content="Overridden title">
<meta property="og:description" content="Overridden description">
<meta property="og:site_name" content="Superhero">

<meta property="og:url" content="https://xp.enonic-qa.com/site/preview/sample-blog/draft/superhero">

<meta property="og:type" content="website">
<meta property="og:locale" content="en"></head>

https://ogp.me/

Add the following fields:

• [ ] og_title (!_allText because title and possibly displayName already in _allText)
• [ ] og_description (_allText)
• [ ] og_site_name (!_allText)
• [ ] og_locale (!_allText)