PoS: fix init chain validator set to respect max_validator_slots param #4427

Job	Run time
build-wasm (ubuntu-20.04, v2, 1.11.0)	6m 53s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 0, namada, v2, tendermint-unreleased-v0...	30m 0s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 1, namada, v2, tendermint-unreleased-v0...	27m 25s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 2, namada, v2, tendermint-unreleased-v0...	30m 49s
namada-release (ubuntu-20.04, 1.11.0, ABCI Release build, namada-e2e-release, v2)	10m 58s
test-wasm (ubuntu-20.04, v2, nightly-2023-06-01, 1.11.0)	7m 28s
namada (ubuntu-20.04, nightly-2023-06-01, 1.11.0, ABCI, namada, v2, tendermint-unreleased-v0.1.4-...	18m 0s
update-wasm	0s
	2h 11m 33s

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