Add segments config + --renderSegments flag

Named segments can be defined in `hugo.toml`.

* Eeach segment consists of zero or more `exclude` filters and zero or more `include` filters.
* Eeach filter consists of one or more field Glob matchers.
* Eeach filter in a section (`exclude` or `include`) is ORed together, each matcher in a filter is ANDed together.

The current list of fields that can be filtered are:

* path as defined in https://gohugo.io/methods/page/path/
* kind
* lang
* output (output format, e.g. html).

It is recommended to put coarse grained filters (e.g. for language and output format) in the excludes section, e.g.:

```toml
[segments.segment1]
  [[segments.segment1.excludes]]
    lang = "n*"
  [[segments.segment1.excludes]]
    no     = "en"
    output = "rss"
  [[segments.segment1.includes]]
    term = "{home,term,taxonomy}"
  [[segments.segment1.includes]]
    path = "{/docs,/docs/**}"
```

By default, Hugo will render all segments, but you can enable filters by setting the `renderSegments` option or `--renderSegments` flag, e.g:

```
hugo --renderSegments segment1,segment2
```

For segment `segment1` in the configuration above, this will:

* Skip rendering of all languages matching `n*`, e.g. `no`.
* Skip rendering of the output format `rss` for the `en` language.
* It will render all pages of kind `home`, `term` or `taxonomy`
* It will render the `/docs` section and all pages below.

Fixes #10106

hugolib/page.go

@@ -22,6 +22,7 @@ import (
 
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/gohugoio/hugo/hugolib/doctree"
+	"github.com/gohugoio/hugo/hugolib/segments"
 	"github.com/gohugoio/hugo/identity"
 	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/output"
@@ -152,6 +153,19 @@ func (p *pageState) reusePageOutputContent() bool {
 	return p.pageOutputTemplateVariationsState.Load() == 1
 }
 
+func (p *pageState) skipRender() bool {
+	b := p.s.conf.C.SegmentFilter.ShouldExcludeFine(
+		segments.SegmentMatcherFields{
+			Path:   p.Path(),
+			Kind:   p.Kind(),
+			Lang:   p.Lang(),
+			Output: p.pageOutput.f.Name,
+		},
+	)
+
+	return b
+}
+
 func (po *pageState) isRenderedAny() bool {
 	for _, o := range po.pageOutputs {
 		if o.isRendered() {