Decide how to configure plaintext and ciphertext parameters

[emmorais]

There are different ways to implement the configuration we need, as can be seen in this discussion.

For example, we could:

• manually configure two separate PolyConfs, and require their degrees to be equal, or
• we could define a degree and two coefficient types, and automatically create two PolyConfs from them.

The goal of this task is to analyze the nuances pointed out in this discussion a implement a solution.

• [ ] define the best approach
• [ ] implement the new configuration
• [ ] refactor the code

[teor2345]

We effectively decided this over PRs #97 and #98.