MM-60351 Use oEmbed for YouTube links (#28312)

* Split up handling of permalinks and other links in getLinkMetadata

* MM-60351 Use oEmbed for YouTube links

* Explicitly request json from the oEmbed provider

* Fix linter

* Fix type of CacheAge field

* Address feedback

server/channels/app/oembed/generator/providers.go.tmpl

@@ -0,0 +1,30 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+// Code generated by "go generate ./channels/app/oembed"
+// DO NOT EDIT
+
+//go:generate go run ./generator/providers_generator.go
+
+package oembed
+
+import (
+	"regexp"
+)
+
+var providers []*ProviderEndpoint
+
+func init() {
+	providers = []*ProviderEndpoint{
+		{{- range .Endpoints }}
+		{
+			URL: "{{ .URL }}",
+			Patterns: []*regexp.Regexp{
+				{{- range .Patterns }}
+				regexp.MustCompile(`{{ . }}`),
+				{{- end }}
+			},
+		},
+		{{- end }}
+	}
+}