MM-13664 Cache external link metadata when populating post metadata (#10128)

* MM-13664 Added LinkMetadata types

* MM-13664 Use LinkMetadata when populating post metadata

* Fix unused import

* Fix index name on SQLite

* Finish adding unit tests

* Address feedback

* Increase max length of URL column to 2048 characters

store/sqlstore/supplier.go

@@ -15,6 +15,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/dyatlov/go-opengraph/opengraph"
 	"github.com/go-sql-driver/mysql"
 	"github.com/lib/pq"
 	"github.com/mattermost/gorp"
@@ -95,6 +96,7 @@ type SqlSupplierOldStores struct {
 	TermsOfService       store.TermsOfServiceStore
 	group                store.GroupStore
 	UserTermsOfService   store.UserTermsOfServiceStore
+	linkMetadata         store.LinkMetadataStore
 }
 
 type SqlSupplier struct {
@@ -145,6 +147,7 @@ func NewSqlSupplier(settings model.SqlSettings, metrics einterfaces.MetricsInter
 	supplier.oldStores.plugin = NewSqlPluginStore(supplier)
 	supplier.oldStores.TermsOfService = NewSqlTermsOfServiceStore(supplier, metrics)
 	supplier.oldStores.UserTermsOfService = NewSqlUserTermsOfServiceStore(supplier)
+	supplier.oldStores.linkMetadata = NewSqlLinkMetadataStore(supplier)
 
 	initSqlSupplierReactions(supplier)
 	initSqlSupplierRoles(supplier)
@@ -183,6 +186,7 @@ func NewSqlSupplier(settings model.SqlSettings, metrics einterfaces.MetricsInter
 	supplier.oldStores.plugin.(*SqlPluginStore).CreateIndexesIfNotExists()
 	supplier.oldStores.TermsOfService.(SqlTermsOfServiceStore).CreateIndexesIfNotExists()
 	supplier.oldStores.UserTermsOfService.(SqlUserTermsOfServiceStore).CreateIndexesIfNotExists()
+	supplier.oldStores.linkMetadata.(*SqlLinkMetadataStore).CreateIndexesIfNotExists()
 
 	supplier.CreateIndexesIfNotExistsGroups()
 
@@ -1032,6 +1036,10 @@ func (ss *SqlSupplier) Group() store.GroupStore {
 	return ss.oldStores.group
 }
 
+func (ss *SqlSupplier) LinkMetadata() store.LinkMetadataStore {
+	return ss.oldStores.linkMetadata
+}
+
 func (ss *SqlSupplier) DropAllTables() {
 	ss.master.TruncateTables()
 }
@@ -1051,6 +1059,10 @@ func (me mattermConverter) ToDb(val interface{}) (interface{}, error) {
 		return model.StringInterfaceToJson(t), nil
 	case map[string]interface{}:
 		return model.StringInterfaceToJson(model.StringInterface(t)), nil
+	case JSONSerializable:
+		return t.ToJson(), nil
+	case *opengraph.OpenGraph:
+		return json.Marshal(t)
 	}
 
 	return val, nil
@@ -1113,6 +1125,10 @@ func (me mattermConverter) FromDb(target interface{}) (gorp.CustomScanner, bool)
 	return gorp.CustomScanner{}, false
 }
 
+type JSONSerializable interface {
+	ToJson() string
+}
+
 func convertMySQLFullTextColumnsToPostgres(columnNames string) string {
 	columns := strings.Split(columnNames, ", ")
 	concatenatedColumnNames := ""