Automate deployment of autopower devices further

[UsualSpec]

We have a deployment process (https://github.com/nsg-ethz/autopower/blob/main/client/README.md) which requires some manual interaction:

• One needs to flash the SD cards operating system
• One needs to sign the client certificates at the CA and need to move the public cert to the Pi

This approach is non optimal and should be more automated.
Agent forwarding could be an approach for signing the certs, but this is still manual.

[UsualSpec]

See https://github.com/nsg-ethz/autopower/blob/main/client/signCerts.sh

[UsualSpec]

@romain-jacob you'd maybe also want to consider the case of recreating/resigning the certificate after a year in signCerts.sh

See

autopower/client/deploy/create_client_cert.sh

Line 10 in cdb4c92

openssl req -new -passin pass:1111 -key client.key -out client.csr -sha512 -subj "/C=CH/ST=Switzerland/L=Zuerich/O=ETH-Zuerich/OU=D-ITET/CN=${CN}"

on how the initial cert creation works.