chore: send referral id in the api (#467)

## Why?

Clear and short explanation here.

## How?

- Done A (replace with a breakdown of the steps)
- Done B
- Done C

## Tickets?

- [Ticket 1](the-ticket-url-here)
- [Ticket 2](the-ticket-url-here)
- [Ticket 3](the-ticket-url-here)

## Contribution checklist?

- [ ] The commit messages are detailed
- [ ] The `build` command runs locally
- [ ] Assets or static content are linked and stored in the project
- [ ] Document filename is named after the slug
- [ ] You've reviewed spelling using a grammar checker
- [ ] For documentation, guides or references, you've tested the
commands and steps
- [ ] You've done enough research before writing

## Security checklist?

- [ ] Sensitive data has been identified and is being protected properly
- [ ] Injection has been prevented (parameterized queries, no eval or
system calls)
- [ ] The Components are escaping output (to prevent XSS)

## References?

Optionally, provide references such as links

## Preview?

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src/components/Eliza/api/index.ts

@@ -242,6 +242,7 @@ export const createSubscription = async (
   projectId?: string,
   productId?: string,
   token?: string,
+  referralId?: string,
 ): Promise<{
   ok: boolean;
   data?: {
@@ -269,6 +270,9 @@ export const createSubscription = async (
             id: productId,
             quantity: 1,
           },
+          metadata: {
+            referralId,
+          },
         }),
       },
     );

src/components/Eliza/components/SubscriptionModal.tsx

@@ -40,8 +40,6 @@ export const SubscriptionModal: React.FC<SubscriptionModalProps> = ({
 
     setIsLoading(true);
 
-    // const referralId = window.promotekit_referral;
-
     const subscriptionCreationResponse = await createSubscription(
       activeProjectId,
       productId,