docs: fix spelling and grammar (#13862)

Fixed various spelling errors and grammatical issues across multiple .mdx documentation files.

www/apps/resources/app/troubleshooting/_sections/api-routes/additional-data.mdx

@@ -7,7 +7,7 @@ If you send a request to an API route and receive the following error:
 }
 ```
 
-## Why this Error Occured
+## Why this Error Occurred
 
 This error occurs when you send the `additional_data` request body parameter to a route that doesn't support it.
 

www/apps/resources/app/troubleshooting/api-routes/additional-data-error/page.mdx

@@ -1,7 +1,7 @@
 import AdditionalDataError from "../../_sections/api-routes/additional-data.mdx"
 
 export const metadata = {
-  title: `Unrecognized fields \`additiona_data\` Error`,
+  title: `Unrecognized fields \`additional_data\` Error`,
 }
 
 # {metadata.title}

www/apps/resources/app/troubleshooting/subscribers/not-working/page.mdx

@@ -74,7 +74,7 @@ If the event is not being emitted, check the logic in your code to ensure that t
 Make sure that your subscriber is correctly set up to listen to the event you're emitting. Check the following:
 
 1. The subscriber is created under the `src/subscribers` directory.
-2. The subscriber exports an asynchronus function that handles the event. For example:
+2. The subscriber exports an asynchronous function that handles the event. For example:
 
 ```ts title="src/subscribers/your-subscriber.ts"
 import { SubscriberArgs, type SubscriberConfig } from "@medusajs/framework"

www/apps/resources/app/troubleshooting/workflow-errors/when-then/page.mdx

@@ -10,7 +10,7 @@ The following error may occur in production if you use a `when-then` block in yo
 custom-workflow:when-then-01JE8Z0M1FXSE2NCK1G04S0RR2:invoke - Handler for action \"when-then-01JE8Z0M1FXSE2NCK1G04S0RR2\" not found...
 ```
 
-## Why this Error Occured
+## Why this Error Occurred
 
 This error occurs if the `when-then` block doesn't return a step's result and doesn't have a name specified.