Adds CustomHTTPErrors ingress annotation and test

Adds per-server/location error-catch functionality to nginx template

Adds documentation

Reduces template duplication with helper function for CUSTOM_ERRORS data

Updates documentation

Adds e2e test for customerrors

Removes AllCustomHTTPErrors, replaces with template function with deduplication and adds e2e test of deduplication

Fixes copy-paste error in test, adds additional test cases

Reverts noop change in controller.go (unused now)

internal/ingress/annotations/customhttperrors/main.go

@@ -0,0 +1,57 @@
+/*
+Copyright 2015 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package customhttperrors
+
+import (
+	"strconv"
+	"strings"
+
+	extensions "k8s.io/api/extensions/v1beta1"
+
+	"k8s.io/ingress-nginx/internal/ingress/annotations/parser"
+	"k8s.io/ingress-nginx/internal/ingress/resolver"
+)
+
+type customhttperrors struct {
+	r resolver.Resolver
+}
+
+// NewParser creates a new custom http errors annotation parser
+func NewParser(r resolver.Resolver) parser.IngressAnnotation {
+	return customhttperrors{r}
+}
+
+// Parse parses the annotations contained in the ingress to use
+// custom http errors
+func (e customhttperrors) Parse(ing *extensions.Ingress) (interface{}, error) {
+	c, err := parser.GetStringAnnotation("custom-http-errors", ing)
+	if err != nil {
+		return nil, err
+	}
+
+	cSplit := strings.Split(c, ",")
+	var codes []int
+	for _, i := range cSplit {
+		num, err := strconv.Atoi(i)
+		if err != nil {
+			return nil, err
+		}
+		codes = append(codes, num)
+	}
+
+	return codes, nil
+}