Plugins: Allow a non-dashboard page to be the default home page (#32926)

* feat: introduce home page redirect if default dashboard

* style: clean up

* Apply suggestions from code review

Co-authored-by: Hugo Häggmark <hugo.haggmark@grafana.com>

* chore(dashboard): remove obsolete setting import

* docs(config): add home_page description

Co-authored-by: Hugo Häggmark <hugo.haggmark@grafana.com>

pkg/setting/setting.go

@@ -366,6 +366,7 @@ type Cfg struct {
 	Quota QuotaSettings
 
 	DefaultTheme string
+	HomePage     string
 
 	AutoAssignOrg     bool
 	AutoAssignOrgId   int
@@ -1252,6 +1253,7 @@ func readUserSettings(iniFile *ini.File, cfg *Cfg) error {
 	LoginHint = valueAsString(users, "login_hint", "")
 	PasswordHint = valueAsString(users, "password_hint", "")
 	cfg.DefaultTheme = valueAsString(users, "default_theme", "")
+	cfg.HomePage = valueAsString(users, "home_page", "")
 	ExternalUserMngLinkUrl = valueAsString(users, "external_manage_link_url", "")
 	ExternalUserMngLinkName = valueAsString(users, "external_manage_link_name", "")
 	ExternalUserMngInfo = valueAsString(users, "external_manage_info", "")