Add an option to send a transaction using all available LBC

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## The Issue

As a daemon or app user, I want to be able to move all my funds from one address to another. Currently, you'd need to send some amount that's smaller than the wallet balance to account for fees. There should be an option that allows all funds to be sent along with the appropriate fee, i.e. a send max scenario.

## Steps

- make it so you can use `all` as a value to `--amount`. this signals you want to use your whole available balance
- create the transaction internally using the full amount, then estimate the fee, then update the transaction to subtract the fee from the full amount

APIs that should support this: `support_create`, `wallet_send`, any other api that has a `--amount` flag

Use case: i want to support my channel with all my available lbc and i don't want to do the math to figure out how much the fee should be.

Take a look `txo_fund --everything`. There may be reusable code there. (https://github.com/lbryio/lbry-sdk/blob/master/lbry/wallet/account.py#L488)

Start in lbry/wallet/account.py around txo_fund --everything, then trace amount handling through support_create, wallet_send, and other APIs with an --amount flag. Compare how transaction creation and fee estimation work, and verify that the supported APIs can send the full available balance with the fee deducted automatically.

Written by the indexing model from the issue text.