Make case study title prefix localizable

Co-authored-by: Dipesh Rawat <rawat.dipesh@gmail.com>

data/i18n/en/en.toml

@@ -18,6 +18,9 @@ other = "Show More Posts..."
 [banner_acknowledgement]
 other = "Hide this notice"
 
+[case_study_prefix]
+other = "Case study:"
+
 [caution]
 other = "Caution:"
 

layouts/case-studies/single.html

@@ -6,7 +6,7 @@
 		<!-- Heading -->
 		<div class="banner {{ if .Params.use_gradient_overlay }}overlay{{ end }}" {{ if isset .Params "heading_background" }}style="background-image: url({{ .Params.heading_background }});"{{ end }}>
 			<h1>
-				<span class="heading">{{ .Params.title_prefix | default "CASE STUDY:" }}</span>
+				<span class="heading">{{ .Params.title_prefix | default ( T "case_study_prefix" ) }}</span>
 				{{- if isset .Params "heading_title_logo" -}}
 					<img class="heading-logo" src="{{ .Params.heading_title_logo}}" />
 				{{- else if isset .Params "heading_title_text" -}}