Payment Methods: enable PPCP method in all environments except test and production

[michaeldcain]

After D165065-code was merged, we started gating the availability of the new PayPal PPCP payment method through the backend (via the shopping cart's allowed_payment_methods and the /me/allowed-payment-methods endpoint). This means that we no longer need to gate the PayPal JS availability via Calypso environment configs.

To enable easier testing of the new payment method, this PR sets the config flag to true in all but the test and production environments. Thus based on the result of the backend's is_paypal_ppcp_enabled(), we'll be able to control which PayPal payment method is available. I left the flags in production and test environments just as a safety precaution.

I've also added a temporary (PPCP) to the new payment method selector to help testers know which method they're using.

To test:
A visual check should suffice, but you can also verify that WPCOM_Billing_PayPal_PPCP or WPCOM_Billing_PayPal_Express is available/unavailable via the shopping cart endpoint based on the configs in D167015-code.

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125508

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125508&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125508&env=a8c-for-agencies

[michaeldcain]

Sort of a duplicate of #96682

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/paypal-ppcp-enabled-environments on your sandbox.