weldr: Add distros/list route

This returns the list of supported distributions as a list of strings.
eg.

{
    distros: ["fedora-33", "fedora-34", "fedora-35"]
}

internal/weldr/api.go

@@ -226,6 +226,7 @@ func setupRouter(api *API) *API {
 	api.router.POST("/api/v:version/upload/providers/save", api.providersSaveHandler)
 	api.router.DELETE("/api/v:version/upload/providers/delete/:provider/:profile", api.providersDeleteHandler)
 
+	api.router.GET("/api/v:version/distros/list", api.distrosListHandler)
 	return api
 }
 
@@ -2955,3 +2956,18 @@ func (api *API) providersDeleteHandler(writer http.ResponseWriter, request *http
 	// TODO: implement this route (it is v1 only)
 	notImplementedHandler(writer, request, params)
 }
+
+func (api *API) distrosListHandler(writer http.ResponseWriter, request *http.Request, params httprouter.Params) {
+	if !verifyRequestVersion(writer, params, 1) {
+		return
+	}
+
+	var reply struct {
+		Distros []string `json:"distros"`
+	}
+	reply.Distros = api.distros.List()
+	sort.Strings(reply.Distros)
+
+	err := json.NewEncoder(writer).Encode(reply)
+	common.PanicOnError(err)
+}

internal/weldr/api_test.go

@@ -71,6 +71,7 @@ func TestBasic(t *testing.T) {
 		{"/api/v0/blueprints/list", http.StatusOK, `{"total":1,"offset":0,"limit":1,"blueprints":["test"]}`},
 		{"/api/v0/blueprints/info/", http.StatusNotFound, `{"errors":[{"code":404,"id":"HTTPError","msg":"Not Found"}],"status":false}`},
 		{"/api/v0/blueprints/info/foo", http.StatusOK, `{"blueprints":[],"changes":[],"errors":[{"id":"UnknownBlueprint","msg":"foo: "}]}`},
+		{"/api/v1/distros/list", http.StatusOK, `{"distros": ["test-distro"]}`},
 	}
 
 	tempdir, err := ioutil.TempDir("", "weldr-tests-")