Resolve where to put Confirmation Height

[rajarshimaitra]

Describe the enhancement
ref: #926 (comment)

We need to find a way to put the transaction's confirmation height in IndexedTxGraph so we can calculate maturity correctly.

[LLFourn]

Put it into the anchor and implement confirmation_height_upper_bound. I think this is already possible in #926.

[danielabrozzoni]

Fixed in #963