staking-miner: balance thresholds

[chevdor]

The staking-miner requires access to a private key to operate.
The account needs no negligeable funds to operate. Those funds are used to:

• make a deposit that is, under normal operations, returned (this is usually a rather significant amount)
• pay for the fees (this is usually rather small

Considering the above, I feel the staking-miner should should have one or a few a fuse mechanisms that allows stopping sending transactions once a threshold is set to prevent draining an account or sending funds away (which has a similar effect since the account will only be able to spend its free balance).

The solution can consist in 2 thresholds:

• lower threshold: if the balance of the acount goes below this threshold, the miner keeps running but no longer submit any solution. If the balance increases again, normal operations resume
• high threshold: if the balance of the account goes above this threshold, some of the funds will automatically be "extracted" from the account and sent to a target account. This option requires a second parameter specifying how much will be transfered out.

cc @kianenigma

[kianenigma]

Sounds like a very interesting addition, added to the project!

[niklasad1]

We got only one "fuse" currently and that is dry-running the transaction and if the account doesn't have sufficient amount of funds the transaction is rejected but it won't help to prevent draining the account.