[MM-34838] Remove Ancillary Permissions That Are Purposefully Being Removed (#17466)

* remove ancillary permissions

* Start writing tests

* Move Ancillary Permissions to FrontEnd

* remove function

* remove test

* clean up

* fix comment

* Update api4/permission.go

Co-authored-by: Martin Kraft <martinkraft@gmail.com>

* Update api4/permission.go

* Update api4/permission.go

* license info

* Add Tests

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Martin Kraft <martinkraft@gmail.com>

api4/permission.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package api4
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+
+	"github.com/mattermost/mattermost-server/v5/model"
+)
+
+func (api *API) InitPermissions() {
+	api.BaseRoutes.Permissions.Handle("/ancillary", api.ApiSessionRequired(appendAncillaryPermissions)).Methods("GET")
+}
+
+func appendAncillaryPermissions(c *Context, w http.ResponseWriter, r *http.Request) {
+	keys, ok := r.URL.Query()["subsection_permissions"]
+
+	if !ok || len(keys[0]) < 1 {
+		c.SetInvalidUrlParam("subsection_permissions")
+		return
+	}
+
+	permissions := strings.Split(keys[0], ",")
+	b, err := json.Marshal(model.AddAncillaryPermissions(permissions))
+	if err != nil {
+		c.SetJSONEncodingError()
+		return
+	}
+	w.Write(b)
+}