Introduce initial block height

[ureeves]

Describe what you want implemented It should be possible to set an "initial block height" to start to cache notes from.

Describe "Why" this is needed As an example, wallets created at a block height of 10000 shouldn't need to start syncing from genesis.

Describe alternatives you've considered N/A

Additional context Does this mean that I always fetch from the beginning if I own no notes?

Maybe it worth to set the key_data.last_height

Originally posted by @herr-seppia in https://github.com/dusk-network/wallet-cli/pull/34#discussion_r863079978