Only create LazyContentProvider for the non-rendering Site

Which saves a fair amound of allocations:

```
gobench --package ./hugolib --bench "SiteNew/Regular_D" --base master
```

Before:

```
name                                  old time/op    new time/op    delta
SiteNew/Regular_Deep_content_tree-10    40.7ms ± 3%    41.2ms ± 1%    ~     (p=0.343 n=4+4)

name                                  old alloc/op   new alloc/op   delta
SiteNew/Regular_Deep_content_tree-10    27.7MB ± 0%    28.8MB ± 0%  +3.76%  (p=0.029 n=4+4)

name                                  old allocs/op  new allocs/op  delta
SiteNew/Regular_Deep_content_tree-10      304k ± 0%      329k ± 0%  +8.07%  (p=0.029 n=4+4)
```

After:

```
name                                  old time/op    new time/op    delta
SiteNew/Regular_Deep_content_tree-10    34.2ms ± 1%    34.7ms ± 1%    ~     (p=0.114 n=4+4)

name                                  old alloc/op   new alloc/op   delta
SiteNew/Regular_Deep_content_tree-10    27.7MB ± 0%    28.1MB ± 0%  +1.38%  (p=0.029 n=4+4)

name                                  old allocs/op  new allocs/op  delta
SiteNew/Regular_Deep_content_tree-10      304k ± 0%      314k ± 0%  +3.03%  (p=0.029 n=4+4)
```

Updates #8919

1 files changed, 4 insertions, 6 deletions

diff --git a/resources/page/page_lazy_contentprovider.go b/resources/page/page_lazy_contentprovider.go
index d8d92d7cd..a513a063a 100644
--- a/resources/page/page_lazy_contentprovider.go
+++ b/resources/page/page_lazy_contentprovider.go
@@ -49,6 +49,10 @@ func NewLazyContentProvider(f func() (ContentProvider, error)) *LazyContentProvi
 	return &lcp
 }
 
+func (lcp *LazyContentProvider) Reset() {
+	lcp.init.Reset()
+}
+
 func (lcp *LazyContentProvider) Content() (interface{}, error) {
 	lcp.init.Do()
 	return lcp.cp.Content()
@@ -67,35 +71,29 @@ func (lcp *LazyContentProvider) PlainWords() []string {
 func (lcp *LazyContentProvider) Summary() template.HTML {
 	lcp.init.Do()
 	return lcp.cp.Summary()
-
 }
 
 func (lcp *LazyContentProvider) Truncated() bool {
 	lcp.init.Do()
 	return lcp.cp.Truncated()
-
 }
 
 func (lcp *LazyContentProvider) FuzzyWordCount() int {
 	lcp.init.Do()
 	return lcp.cp.FuzzyWordCount()
-
 }
 
 func (lcp *LazyContentProvider) WordCount() int {
 	lcp.init.Do()
 	return lcp.cp.WordCount()
-
 }
 
 func (lcp *LazyContentProvider) ReadingTime() int {
 	lcp.init.Do()
 	return lcp.cp.ReadingTime()
-
 }
 
 func (lcp *LazyContentProvider) Len() int {
 	lcp.init.Do()
 	return lcp.cp.Len()
-
 }