add --fee-included flag to `siac wallet send siacoins`

MERGE REQUEST

Overview

Add a flag which allows sending an amount as-is, with the fees included. This allows sending e.g. an exact wallet balance.

Example for Visual changes (ie Screenshot)

Sending with and without the flag (note that the first send takes a while, skip ahead): https://asciinema.org/a/IByHeNkpquMoxOZ3Fen4N01GY

Issues Closed

#3849 (closed)

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods, or updating methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to work flow
• Issue added to Sia-UI repo for new supporting features
• Changelog updated