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/endpoint.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package oembed
+
+import (
+	"net/url"
+	"regexp"
+)
+
+//go:generate go run ./generator/providers_generator.go
+
+type ProviderEndpoint struct {
+	URL      string
+	Patterns []*regexp.Regexp
+}
+
+func (e *ProviderEndpoint) GetProviderURL(requestURL string) string {
+	// This error is checked when generating the list of providers
+	url, _ := url.Parse(e.URL)
+
+	query := url.Query()
+	query.Add("format", "json")
+	query.Add("url", requestURL)
+	url.RawQuery = query.Encode()
+
+	return url.String()
+}
+
+// FindEndpointForURL returns a ProviderEndpoint for a given URL if it matches one that's supported by us. Returns nil
+// if none of the supported providers match the given URL.
+func FindEndpointForURL(requestURL string) *ProviderEndpoint {
+	for _, provider := range providers {
+		for _, pattern := range provider.Patterns {
+			if pattern.MatchString(requestURL) {
+				return provider
+			}
+		}
+	}
+
+	return nil
+}