feat(billing): Add Seer to CheckoutAPIData (#91775)

Closes:
https://linear.app/getsentry/issue/BIL-529/add-seer-to-the-checkout-request-on-form-submit

Adds the Seer boolean flag from the form data into the checkout request

Author: jarrettscott

static/gsApp/views/amCheckout/types.tsx

@@ -37,6 +37,7 @@ export type CheckoutAPIData = BaseCheckoutData & {
   reservedSpans?: number;
   reservedTransactions?: number;
   reservedUptime?: number;
+  seer?: boolean;
 };
 
 export type StepProps = {

static/gsApp/views/amCheckout/utils.tsx

@@ -479,6 +479,9 @@ export function getCheckoutAPIData({
     referrer: referrer || 'billing',
     ...(previewToken && {previewToken}),
     ...(paymentIntent && {paymentIntent}),
+    ...(formData.seerEnabled && {
+      seer: formData.seerEnabled,
+    }),
   };
 
   if (formData.applyNow) {