Mint: add max balance setting #84

Job	Run time
checks / formatting	22s
checks / ruff	7s
checks / mypy	35s
regtest (3.10, 1.5.1, LNbitsWallet) / regtest	2m 36s
regtest (3.10, 1.5.1, LndRestWallet) / regtest	2m 34s
regtest (3.10, 1.5.1, CoreLightningRestWallet) / regtest	2m 50s
tests (ubuntu-latest, 3.10, 1.5.1, FakeWallet) / poetry	1m 27s
tests (ubuntu-latest, 3.9, 1.5.1, FakeWallet) / poetry	1m 25s
	11m 56s

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