template: Use cases.Title instead of deprecated strings.Title (#15721)

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

docs/configuration/template_reference.md

@@ -68,7 +68,7 @@ versions.
 
 | Name          | Arguments     | Returns |    Notes    |
 | ------------- | ------------- | ------- | ----------- |
-| title         | string        | string  | [strings.Title](https://golang.org/pkg/strings/#Title), capitalises first character of each word.|
+| title         | string        | string  | [cases.Title](https://pkg.go.dev/golang.org/x/text/cases#Title), capitalises first character of each word.|
 | toUpper       | string        | string  | [strings.ToUpper](https://golang.org/pkg/strings/#ToUpper), converts all characters to upper case.|
 | toLower       | string        | string  | [strings.ToLower](https://golang.org/pkg/strings/#ToLower), converts all characters to lower case.|
 | stripPort     | string        | string  | [net.SplitHostPort](https://pkg.go.dev/net#SplitHostPort), splits string into host and port, then returns only host.|

template/template.go

@@ -30,6 +30,8 @@ import (
 	"github.com/grafana/regexp"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
 
 	common_templates "github.com/prometheus/common/helpers/templates"
 
@@ -166,7 +168,7 @@ func NewTemplateExpander(
 				return html_template.HTML(text)
 			},
 			"match":     regexp.MatchString,
-			"title":     strings.Title, //nolint:staticcheck // TODO(beorn7): Need to come up with a replacement using the cases package.
+			"title":     cases.Title(language.AmericanEnglish, cases.NoLower).String,
 			"toUpper":   strings.ToUpper,
 			"toLower":   strings.ToLower,
 			"graphLink": strutil.GraphLinkForExpression,