PoS: keep 2 past epochs of data by default #4566

Job	Run time
build-wasm (ubuntu-20.04, v2, 1.11.0)	4m 18s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 0, namada, v2, namada-release (ubuntu-2...	28m 30s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 1, namada, v2, namada-release (ubuntu-2...	27m 3s
namada-e2e (ubuntu-20.04, nightly-2023-06-01, 1.7.0, e2e, 2, namada, v2, namada-release (ubuntu-2...	30m 39s
namada-release (ubuntu-20.04, 1.11.0, ABCI Release build, namada-e2e-release, v2)	10m 36s
test-wasm (ubuntu-20.04, v2, nightly-2023-06-01, 1.11.0)	8m 1s
namada (ubuntu-20.04, nightly-2023-06-01, 1.11.0, ABCI, namada, v2, tendermint-unreleased-v0.1.4-...	13m 37s
update-wasm	0s
	2h 2m 44s

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