fix: redirect-paypro-to-thank-you is called as a POST request

[gibertoni]

After I purchased the Pro license, I got the following error in the browser checkout:

Cannot POST /api/redirect-paypro-to-thank-you

It seems like a simple patch since the API is listening to a GET instead of a POST

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Guilherme Gibertoni seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[pimterry]

Good catch thanks @gibertoni! I've definitely tested this in the past and it has used GET, so I suspect PayPro have multiple flows here for different scenarios, or they've changed something internally. In either case, we should support both GET & POST to handle this. Unfortunately PayPro's docs are terrible so it's not totally clear how this works, but we can support both easily so that's OK. Can you update this to do that?

Please also sign the CLA so this can be merged, it's very short: it just confirms it's your code, you have the rights to contribute it (it's not employer property or similar) and you're happy to give it to the project.