This ommmit contains some security hardening measures for the Hugo build runtime.
There are some rarely used features in Hugo that would be good to have disabled by default. One example would be the "external helpers".
For `asciidoctor` and some others we use Go's `os/exec` package to start a new process.
These are a predefined set of binary names, all loaded from `PATH` and with a predefined set of arguments. Still, if you don't use `asciidoctor` in your project, you might as well have it turned off.
You can configure your own in the new `security` configuration section, but the defaults are configured to create a minimal amount of site breakage. And if that do happen, you will get clear instructions in the loa about what to do.
The default configuration is listed below. Note that almost all of these options are regular expression _whitelists_ (a string or a slice); the value `none` will block all.
```toml
[security]
enableInlineShortcodes = false
[security.exec]
allow = ['^dart-sass-embedded$', '^go$', '^npx$', '^postcss$']
osEnv = ['(?i)^(PATH|PATHEXT|APPDATA|TMP|TEMP|TERM)$']
[security.funcs]
getenv = ['^HUGO_']
[security.http]
methods = ['(?i)GET|POST']
urls = ['.*']
```
The main motivation behind this is simplicity and correctnes, but the new small config library is also faster:
```
BenchmarkDefaultConfigProvider/Viper-16 252418 4546 ns/op 2720 B/op 30 allocs/op
BenchmarkDefaultConfigProvider/Custom-16 450756 2651 ns/op 1008 B/op 6 allocs/op
```
Fixes#8633Fixes#8618Fixes#8630
Updates #8591Closes#6680Closes#5192
Updates #7777
Added support to allow SourceMap files to be external to the build.
In addition added more information when the js compilation has an error.
Correctly append sourceMappingURL to output file.
Fix merge conflict.
