go: sqle: cluster: Create missing remotes for cluster replication on startup if they do not already exist.

Previously `dolt sql-server` would error if there were existing databases and
they were missing any of the remotes listed as cluster replication remotes in
the config.yaml. This changes it so that those remotes are automatically
created at startup instead.

go/libraries/doltcore/sqle/cluster/controller.go

@@ -299,9 +299,14 @@ func (c *Controller) applyCommitHooks(ctx context.Context, name string, bt *sql.
 	dialprovider := c.gRPCDialProvider(denv)
 	var hooks []*commithook
 	for _, r := range c.cfg.StandbyRemotes() {
+		remoteUrl := strings.Replace(r.RemoteURLTemplate(), dsess.URLTemplateDatabasePlaceholder, name, -1)
 		remote, ok := remotes.Get(r.Name())
 		if !ok {
-			return nil, fmt.Errorf("sqle: cluster: standby replication: destination remote %s does not exist on database %s", r.Name(), name)
+			remote = env.NewRemote(r.Name(), remoteUrl, nil)
+			err := denv.AddRemote(remote)
+			if err != nil {
+				return nil, fmt.Errorf("sqle: cluster: standby replication: could not create remote %s for database %s: %v", r.Name(), name, err)
+			}
 		}
 		commitHook := newCommitHook(c.lgr, r.Name(), remote.Url, name, c.role, func(ctx context.Context) (*doltdb.DoltDB, error) {
 			return remote.GetRemoteDB(ctx, types.Format_Default, dialprovider)

integration-tests/go-sql-server-driver/tests/sql-server-cluster.yaml

@@ -1736,3 +1736,89 @@ tests:
   - on: server1
     queries:
     - exec: "call dolt_assume_cluster_role('primary', '3')"
+# Assert that we can add a new standby to an existing server and bring the server up.
+- name: adding new remotes to the config creates those remotes on startup
+  multi_repos:
+  - name: server1
+    with_files:
+    - name: onestandby.yaml
+      contents: |
+        log_level: trace
+        listener:
+          host: 0.0.0.0
+          port: 3309
+        cluster:
+          standby_remotes:
+          - name: standby_one
+            remote_url_template: http://localhost:3852/{database}
+          bootstrap_role: primary
+          bootstrap_epoch: 1
+          remotesapi:
+            port: 3851
+    - name: twostandbys.yaml
+      contents: |
+        log_level: trace
+        listener:
+          host: 0.0.0.0
+          port: 3309
+        cluster:
+          standby_remotes:
+          - name: standby_one
+            remote_url_template: http://localhost:3852/{database}
+          - name: standby_two
+            remote_url_template: http://localhost:3853/{database}
+          bootstrap_role: primary
+          bootstrap_epoch: 1
+          remotesapi:
+            port: 3851
+    server:
+      args: ["--config", "onestandby.yaml"]
+      port: 3309
+  - name: standby
+    with_files:
+    - name: config.yaml
+      contents: |
+        log_level: trace
+        listener:
+          host: 0.0.0.0
+          port: 3310
+        cluster:
+          standby_remotes:
+          - name: standby
+            remote_url_template: http://localhost:3851/{database}
+          bootstrap_role: standby
+          bootstrap_epoch: 1
+          remotesapi:
+            port: 3853
+    server:
+      args: ["--config", "config.yaml"]
+      port: 3310
+  connections:
+  - on: server1
+    queries:
+    - exec: "create database testdb"
+  - on: server1
+    restart_server:
+      args: ["--config", "twostandbys.yaml"]
+  - on: server1
+    queries:
+    - exec: "use testdb"
+    - query: "select count(*) from dolt_remotes"
+      result:
+        columns: ["count(*)"]
+        rows:
+        - ["2"]
+    - exec: 'SET @@GLOBAL.dolt_cluster_ack_writes_timeout_secs = 1'
+    - exec: "create table vals (id int primary key)"
+    - query: "show warnings"
+      result:
+        columns: ["Level", "Code", "Message"]
+        rows:
+        - ["Warning", "3024", "Timed out replication of commit to 1 out of 2 replicas."]
+  - on: standby
+    queries:
+    - query: "select count(*) from `testdb`.`vals`"
+      result:
+        columns: ["count(*)"]
+        rows:
+        - ["0"]