imagestorage: fix templating of public_url option for webdav (#74885)

* spelling in error message

* imguploader: fix template for webdav url

Since a few years ago, when loading the config file, the  template gets replaced in the expanding
env var phase (see ##25075) and introduced a bug in the webdav public_url config option. This commit
changes the template syntax to be {{file}}. This doesn't get expanded and removed when the config file
is loaded.

* devenv: add a block for a WebDAV server

* Adding alerting as codeowners for webdav

---------

Co-authored-by: Timur Olzhabayev <timur.olzhabayev@grafana.com>

pkg/components/imguploader/webdavuploader.go

@@ -37,8 +37,8 @@ var netClient = &http.Client{
 }
 
 func (u *WebdavUploader) PublicURL(filename string) string {
-	if strings.Contains(u.public_url, "${file}") {
-		return strings.ReplaceAll(u.public_url, "${file}", filename)
+	if strings.Contains(u.public_url, "{{file}}") {
+		return strings.ReplaceAll(u.public_url, "{{file}}", filename)
 	}
 
 	publicURL, _ := url.Parse(u.public_url)