Add genesis state for channel/v2

[DimitrisJim]

Add genesis state for channel/v2 state entries. Judging by what we imported/exported for v1, we should still be doing something similar for v2, a rough proto might look like:

// GenesisState defines the ibc channel submodule's genesis state.
message GenesisState {
  // TODO: Possibly re-use?
  repeated IdentifiedChannel channels = 1 [(gogoproto.casttype) = "IdentifiedChannel", (gogoproto.nullable) = false];
  repeated PacketState       acknowledgements = 2 [(gogoproto.nullable) = false];
  repeated PacketState       commitments      = 3 [(gogoproto.nullable) = false];
  repeated PacketState       receipts         = 4 [(gogoproto.nullable) = false];
  repeated PacketSequence    send_sequences   = 5 [(gogoproto.nullable) = false];
}

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[DimitrisJim]

Gonna do as much of this as I can until weds. Splitting up into:

• Add protobuf file + necessary type helpers (validation, constructors etc) if needed.
• Add necessary keeper funcs + tests for them.
• Add submodule's genesis.go and tests for it.

[DimitrisJim]

Unsure how genesis will look with new proposed aliasing approach. Leaving issue as is for now.

[AdityaSripal]

• Add protobuf file + necessary type helpers (validation, constructors etc) if needed.
• Add necessary keeper funcs + tests for them.
• Add submodule's genesis.go and tests for it.

[gjermundgaraba]

Closed in favor of #7922