Add devnet support to forest-tool api serve and document the functionality

[lemmih]

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[LesnyRumcajs]

These need to be ported to forest-tool api serve

forest/scripts/devnet/docker-compose.yml

Lines 200 to 206 in ded933f

	set -euxo pipefail
	if [ ! -f ${FOREST_DATA_DIR}/forest_config.toml ]; then
	export NETWORK_NAME=$$(grep -o \"localnet.*\" ${LOTUS_DATA_DIR}/localnet.json)
	cp /forest/forest_config.toml.tpl ${FOREST_DATA_DIR}/forest_config.toml
	echo name = $$NETWORK_NAME >> ${FOREST_DATA_DIR}/forest_config.toml
	fi
	forest --genesis ${LOTUS_DATA_DIR}/devgen.car --config ${FOREST_DATA_DIR}/forest_config.toml --save-token ${FOREST_DATA_DIR}/token.jwt --rpc-address 0.0.0.0:${FOREST_RPC_PORT}

[LesnyRumcajs]

Linked to #4598, given one is hardly useful without the other.