Adding unit tests for ISO15118-2 messages

### ISO Version

ISO15118-2

### Describe the problem

It would be very useful for the library to have unit tests for each V2G message.

In the following table you will find the XML file and the corresponding EXI stream for each ISO-2 message.

| Message | Files | Done |
| -------- | ------- | ------- |
| SessionSetupReq | [SessionSetupReq.zip](https://github.com/EVerest/libcbv2g/files/14573704/SessionSetupReq.zip) | :x: |
| SessionSetupRes | [SessionSetupRes.zip](https://github.com/EVerest/libcbv2g/files/14573708/SessionSetupRes.zip) | :x: |
| ServiceDiscoveryReq | [ServiceDiscoveryReq.zip](https://github.com/EVerest/libcbv2g/files/14573710/ServiceDiscoveryReq.zip)| :x: |
| ServiceDiscoveryRes | [ServiceDiscoveryRes.zip](https://github.com/EVerest/libcbv2g/files/14573714/ServiceDiscoveryRes.zip) | :x: |
| ServiceDetailReq | | :x: |
| ServiceDetailRes | | :x: |
| PaymentServiceSelectionReq | [PaymentServiceSelectionReq.zip](https://github.com/EVerest/libcbv2g/files/14573716/PaymentServiceSelectionReq.zip)| :x: |
| PaymentServiceSelectionRes |[PaymentServiceSelectionRes.zip](https://github.com/EVerest/libcbv2g/files/14573717/PaymentServiceSelectionRes.zip)| :x: |
| CertificateUpdateReq | | :x: |
| CertificateUpdateRes | | :x: |
| CertificateInstallationReq | | :x: |
| CertificateInstallationRes | | :x: |
| PaymentDetailsReq | | :x: |
| PaymentDetailsRes | | :x: |
| AuthorizationReq | | :x: |
| AuthorizationRes | | :x: |
| ChargeParameterDiscoveryReq | | :x: |
| ChargeParameterDiscoveryRes | | :x: |
| PowerDeliveryReq | | :x: |
| PowerDeliveryRes | | :x: |
| SessionStopReq | | :x: |
| SessionStopRes | | :x: |
| MeteringReceiptReq | | :x: |
| MeteringReceiptRes | | :x: |
| ChargingStatusReq | | :x: |
| ChargingStatusRes | | :x: |
| CableCheckReq | | :x: |
| CableCheckRes | | :x:|
| PreChargeReq | | :x: |
| PreChargeRes || :x: |
| CurrentDemandReq | | :x: |
| CurrentDemandRes | | :x: |
| WeldingDetectionReq | | :x: |
| WeldingDetectionRes | | :x: |

### Describe your solution

Create for every message a encode and decode test with the help of XML and EXI messages.

A sample of how the tests can be written can be found in the `tests/app_handshake` folder.

### Additional context

Attention: Not all EXI & XML messages uploaded yet