feat(renterd): bulk rescan hosts #2796

Job	Run time
test	5m 58s
test-go (ubuntu-latest, ./renterd)	45s
test-go (ubuntu-latest, ./hostd)	50s
test-go (ubuntu-latest, ./walletd)	51s
test-go (macos-latest, ./renterd)	51s
test-go (macos-latest, ./hostd)	52s
test-go (macos-latest, ./walletd)	49s
test-go (windows-latest, ./renterd)	1m 41s
test-go (windows-latest, ./hostd)	1m 23s
test-go (windows-latest, ./walletd)	1m 42s
e2e / explorer-e2e-shard-tests (1, 4) / test-e2e	1m 51s
e2e / explorer-e2e-shard-tests (2, 4) / test-e2e	1m 43s
e2e / explorer-e2e-shard-tests (3, 4) / test-e2e	1m 36s
e2e / explorer-e2e-shard-tests (4, 4) / test-e2e	1m 41s
e2e / hostd-e2e-shard-tests (1, 4) / test-e2e	1m 46s
e2e / hostd-e2e-shard-tests (2, 4) / test-e2e	1m 50s
e2e / hostd-e2e-shard-tests (3, 4) / test-e2e	1m 36s
e2e / hostd-e2e-shard-tests (4, 4) / test-e2e	1m 47s
e2e / renterd-e2e-shard-tests (1, 4) / test-e2e	3m 19s
e2e / renterd-e2e-shard-tests (2, 4) / test-e2e	3m 14s
e2e / renterd-e2e-shard-tests (4, 4) / test-e2e	3m 28s
e2e / walletd-e2e-shard-tests (1, 4) / test-e2e	1m 42s
e2e / walletd-e2e-shard-tests (2, 4) / test-e2e	1m 43s
e2e / walletd-e2e-shard-tests (3, 4) / test-e2e	1m 37s
e2e / walletd-e2e-shard-tests (4, 4) / test-e2e	1m 39s
e2e / renterd-e2e-shard-tests (3, 4) / test-e2e	3m 30s
e2e / walletd-e2e-merge-reports / merge-reports	5s
e2e / hostd-e2e-merge-reports / merge-reports	6s
e2e / explorer-e2e-merge-reports / merge-reports	9s
e2e / renterd-e2e-merge-reports / merge-reports	7s
	50m 11s

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