go.mod: update to github.com/emicklei/go-restful/v3 v3.7.3

full diff: https://github.com/emicklei/go-restful/compare/v2.9.5...v3.7.3

- Switch to using go modules
- Add check for wildcard to fix CORS filter
- Add check on writer to prevent compression of response twice
- Add OPTIONS shortcut WebService receiver
- Add Route metadata to request attributes or allow adding attributes to routes
- Add wroteHeader set
- Enable content encoding on Handle and ServeHTTP
- Feat: support google custom verb
- Feature: override list of method allowed without content-type
- Fix Allow header not set on '405: Method Not Allowed' responses
- Fix Go 1.15: conversion from int to string yields a string of one rune
- Fix WriteError return value
- Fix: use request/response resulting from filter chain
- handle path params with prefixes and suffixes
- HTTP response body was broken, if struct to be converted to JSON has boolean value
- List available representations in 406 body
- Support describing response headers
- Unwrap function in filter chain + remove unused dispatchWithFilters

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/emicklei/go-restful/v3/extensions.go

@@ -0,0 +1,21 @@
+package restful
+
+// Copyright 2021 Ernest Micklei. All rights reserved.
+// Use of this source code is governed by a license
+// that can be found in the LICENSE file.
+
+// ExtensionProperties provides storage of vendor extensions for entities
+type ExtensionProperties struct {
+	// Extensions vendor extensions used to describe extra functionality
+	// (https://swagger.io/docs/specification/2-0/swagger-extensions/)
+	Extensions map[string]interface{}
+}
+
+// AddExtension adds or updates a key=value pair to the extension map.
+func (ep *ExtensionProperties) AddExtension(key string, value interface{}) {
+	if ep.Extensions == nil {
+		ep.Extensions = map[string]interface{}{key: value}
+	} else {
+		ep.Extensions[key] = value
+	}
+}