Backend work for #1859
- Remove file count from qa stats endpoint
- Compute isFile or isError per page when page is added
- Increment filePageCount and errorPageCount per crawl to count number of isFile or isError pages
- Add file and error counts to crawl replay.json endpoint (filePageCount and errorPageCount)
- Add migration 0028 to set isFile / isError for each page, aggregate filePageCount / errorPageCount per crawl
- Determine if page is a file based on loadState == 2, mime type or status code and lack of title
