add sats_per_kweight option when crafting a transaction

[ziggie1984]

For the commands SendCoins, SendMany, CloseChannel, OpenChannel, BatchOpenChannel and in the response of the EstimateFee command the option sats_per_kweight is added to allow for more granular control of fees when creating transactions.

In the current fee environment one cannot use decimal fee estimates for sats_per_vbyte, therefore using sats_per_kweight one will be able to use decimal sats_per_vbyte feerates indirectly without introducing floating point math.

Currently in the lnd backend the option sats_per_kweight is prioritized in case both options are present at the same time (sats_per_kweight and sats_per_vbyte). Though having both of them set is prevented on lncli level. This might be open for discussion.

Steps to Test

Changes where done on the rpc level and lncli therefore Polar was used to test all the changed commands.

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