`EnableBankingIntegration.certificate` should be named `EnableBankingIntegration.key`

[ivan-holvi]

Here we use certificate as naming, but in reality it is a key.

enablebanking-python-sdk/src/enablebanking_sdk/service/integration.py

Line 22 in d915bde

certificate: str

Leaving this issue as a reminder for myself to change it.

Extra: If we release a change with this, it should be either a major to point out there are breaking changes or keep both parameters for backwards compatibility.