Move from embedded FHE keys to configurable keys

[dartdart26]

Currently, FHE keys are embedded in the go binaries. We should move to keys that can be read at runtime.

There are 3 FHE keys:

• evaluation key (sks) - this is a key that should be available to all nodes and should be public. I think it is fine if node just read it from disk. It could also be made available publicly or somehow in the KMS (because it corresponds to a particular public/secret keypair - please correct if wrong).
• public key (pks) - also public and should be available to all nodes such that they can serve it to clients over Eth RPC. Also, could be made publicly available in a different manner and also be part of the KMS interface.
• secret key (cks) - currently, we want it to be available to all nodes such that they can do decryption/reencryption. However, once there is a KMS, these operations will be done in the KMS. We should find a way to abstract that such that we use the KMS interface, but still make the full secret key available to every node (until the KMS is available).

Add a functionality to generate the keys such that tests can run with them. Also, keys can be used by users of fhemv-go.

[youben11]

solved in #20