Use getIntegrationByName API for Replay docs (#8960)

Author: AbhiPrasad

src/platforms/javascript/common/session-replay/understanding-sessions.mdx

@@ -64,7 +64,7 @@ Sentry.init({
 });
 
 // You can access the active replay instance from anywhere in your code like this:
-const replay = Sentry.getClient().getIntegrationById("Replay");
+const replay = Sentry.getClient().getIntegrationByName("Replay");
 
 // This starts in `session` mode, regardless of sample rates
 replay.start();
@@ -134,7 +134,7 @@ Sentry.init({
 // Check if user is an employee, if so, always record a replay
 if (loggedInUser.isEmployee) {
   // You can get a reference to the Sentry Replay integration like so:
-  const replay = Sentry.getClient().getIntegrationById("Replay");
+  const replay = Sentry.getClient().getIntegrationByName("Replay");
 
   replay.flush();
 }