[DTPPCPSDK-2824] [DTPRP-1734] [DTPRP-1751] Limit eligible button to Paypal when new createSubscription is used

[9zees]

Description

This PR is for this JIRA: https://paypal.atlassian.net/browse/DTPPCPSDK-2824

We need to evaluate 3 conditions to check if we are handling a Full-Stack Subscription (not NextGen Subscription or any other flows like createOrders, createVaultSetupToken, etc).

Condition 1: createSubscription callback must have been passed. It cannot be undefined or null.
Condition 2: sdkToken must have been passed. It cannot be undefined or null.
Condition 3: intent cannot equal to "subscription".

When all 3 conditions have been met, the isFsSubscription flag should evaluate to true.

This is the flag that we use to only display 1 PayPal payment button if it's a Full-Stack Subscription.

Why are we making these changes? Include references to any related Jira tasks or GitHub Issues

JIRA: https://paypal.atlassian.net/browse/DTPPCPSDK-2824
We are making this change to support the new Fullstack Subscription.

Reproduction Steps (if applicable)

http://localhost.paypal.com:8080/xo-integrations/paypal/subscriptions

Screenshots (if applicable)

Here we can see that only 1 PayPal button is being shown, and nothing else.

Dependent Changes (if applicable)

Groups who should review (if applicable)

❤️ Thank you!

[codecov]

Codecov Report

Attention: Patch coverage is 46.87500% with 17 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@f0b5eeb). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/zoid/buttons/component.jsx	5.88%	15 Missing and 1 partial ⚠️
src/ui/buttons/buttons.jsx	92.85%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2456   +/-   ##
=======================================
  Coverage        ?   56.54%           
=======================================
  Files           ?      150           
  Lines           ?    13209           
  Branches        ?      814           
=======================================
  Hits            ?     7469           
  Misses          ?     5638           
  Partials        ?      102           

Flag	Coverage Δ
jest	31.50% <75.00%> (?)
karma	54.36% <62.50%> (?)
vitest	51.53% <46.87%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.