installer: use `-rpcauth` for managed bitcoind #1826

Job	Run time
linter	34s
linter_gui	1m 29s
unit_tests (1.63, ubuntu-latest)	2m 57s
unit_tests (1.63, macOS-latest)	3m 25s
unit_tests (1.63, windows-latest)	3m 43s
unit_tests (nightly, ubuntu-latest)	51s
unit_tests (nightly, macOS-latest)	1m 33s
unit_tests (nightly, windows-latest)	1m 44s
unit_tests_gui	0s
	16m 16s

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