Move HTTP service to public for plugin use (#27284)

* Move httpservice for use in plugins

* Adapt httpservice for plugin use

* Fix lint

server/channels/app/server.go

@@ -28,6 +28,7 @@ import (
 	"golang.org/x/crypto/acme/autocert"
 
 	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/httpservice"
 	"github.com/mattermost/mattermost/server/public/shared/i18n"
 	"github.com/mattermost/mattermost/server/public/shared/mlog"
 	"github.com/mattermost/mattermost/server/public/shared/request"
@@ -66,7 +67,6 @@ import (
 	"github.com/mattermost/mattermost/server/v8/einterfaces"
 	"github.com/mattermost/mattermost/server/v8/platform/services/awsmeter"
 	"github.com/mattermost/mattermost/server/v8/platform/services/cache"
-	"github.com/mattermost/mattermost/server/v8/platform/services/httpservice"
 	"github.com/mattermost/mattermost/server/v8/platform/services/remotecluster"
 	"github.com/mattermost/mattermost/server/v8/platform/services/searchengine/bleveengine"
 	"github.com/mattermost/mattermost/server/v8/platform/services/searchengine/bleveengine/indexer"