rfc: add end-to-end testing RFC (#5337)
rfc: add end-to-end testing RFC (#5337)

[Rendered](https://github.com/tendermint/tendermint/blob/erik/rfc-e2e-testing/docs/rfc/rfc-001-end-to-end-testing.md).

Related to #5291.
tendermint/tendermint,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint