[docs] indexing improvements

[paulOsinski]

1. robots.txt was blocking the /admin/ directory from search crawling, this overrides this behavior. (/admin/ is a documentation folder, not anything sensitive)
2. I want our search indexer Algolia to know the "audience" of a page for improved search UX, this adds a tag that pulls that from the front matter
3. latest release version was caching at build time and not refreshing - this sets a Hugo variable to call the API again every hour to get the latest DD version (for the header)

[mtesauro]

Approved