common/herrors: Make the file error log format configurable

common/herrors: Make the file error log format configurable

Will check for an OS environment variable named `HUGO_FILE_LOG_FORMAT`.

The tokens available are `:file` (absolute filename), `:line` (line number) and `:col` (column number).

The default format is: \":file::line::col\"`

How to set OS environment variables is OS specific, but an example on Unix setting an alternative format when running Hugo:

```bash
env HUGO_FILE_LOG_FORMAT="\":file::line\"" hugo
```

The above will include filename and line number quoted.

Fixes #5352