Add code-level (.cpp) comments for advanced crypto capabilities

[yspolyakov]

In particular, the following capabilities should be documented

• Hoisting and fast rotations
• CKKS bootstrapping
• Key switching (specifically hybrid key switching)

The goal is to make it easier for advanced developers to write their own efficient examples, especially when no examples for advanced capabilities are available.

As part of this, also make addFirst = true the default option of EvalFastRotationExt.