API inconsistency in netmap

[roman-khimov]

One can get network settings or node info via the netmap service, but there is no way to change any of them. API tries to hide blockchain details, but fails to do that because changes require good old Neo transactions via JSON-RPC connections.

[cthulhu-rider]

also

neofs-api/netmap/service.proto

Lines 37 to 43 in dcead71

	// Returns network map snapshot of the current NeoFS epoch.
	//
	// Statuses:
	// - **OK** (0, SECTION_SUCCESS):
	// information about the current network map has been successfully read;
	// - Common failures (SECTION_FAILURE_COMMON).
	rpc NetmapSnapshot (NetmapSnapshotRequest) returns (NetmapSnapshotResponse);

allows to request only the current network map, while https://pkg.go.dev/github.com/nspcc-dev/neofs-contract@v0.19.1/netmap#SnapshotByEpoch is time-based