Make selection of leaf certificate configurable

[Pietfried]

Describe the problem

There seem to be different requirements and use cases of how a leaf certificate (SECC or CSMS) shall be selected in case multiple valid certificates are present on the charger.

The current mechanism is to select the certificate with the latest validTo property. However, OCPP requires

The Charge Point SHALL switch to the new certificate as soon as the current date and
time is after the ‘Not valid before’ field in the certificate

This currently causes some OCTT test cases to fail.

Describe your solution

Make the selection mechanism configurable (differntiate between validTo or validFrom to be decisive), to be able to address all use cases.

Additional context

No response