Hugo: default search input placeholder

When no contentType was used, the search input showed
"Search in <no value". There only is a contentType when using the
search shortcode.

- Default placeholder is now "Search in cuelang.org" (/search/?q=)
- When using the search shortcode with a contentType, you see
eg. "Search in How-to Guides"  (/examples/shortcodes/search/)

For https://linear.app/usmedia/issue/CUE-344

Closes #433 as merged as of commit 730d0b4c.

Signed-off-by: Anne van Gorkom <[email protected]>
Change-Id: Icd38ad5530f7fa3ea4415a164474485e5686884c
Dispatch-Trailer: {"type":"trybot","CL":1172175,"patchset":1,"ref":"refs/changes/75/1172175/1","targetBranch":"alpha"}

hugo/i18n/en.toml

@@ -94,6 +94,8 @@ other = "documents found"
 [search_filters_title]
 other = "Filters"
 [search_placeholder]
+other = "Search in cuelang.org"
+[search_placeholder_content_type]
 other = "Search in {{ .contentType }}"
 
 [search_tags_title]

hugo/layouts/partials/search.html

@@ -3,7 +3,11 @@
 {{ $contentTypes := slice }}
 {{ $contentType := .contentType | default "" }}
 {{ $type := .type | default "full" }}
-{{ $placeholder := (T "search_placeholder" .) }}
+{{ $placeholder := (T "search_placeholder" ) }}
+
+{{ if $contentType }}
+    {{ $placeholder = (T "search_placeholder_content_type" .) }}
+{{ end }}
 
 {{ with $context }}
     {{ if $showContentTypes }}