Response of GET /api/v1/messages/{message_id}/metadata.
Returns the metadata of a message.
### messageId(): String
The message id of this message
### parentMessageIds(): String[]
The ids of the parents of this message
### isSolid(): boolean
IF this message is solid
### referencedByMilestoneIndex(): long
The optional milestone index if this message is referenced
### milestoneIndex(): long
The optional milestone index this was included in
### ledgerInclusionState(): Optional<[LedgerInclusionStateDto](#ledgerinclusionstatedto)>
The ledger state
### conflictReason(): int
The optional reason of conflict
### shouldPromote(): Optional<Boolean>
Optional; if the message needs to be promoted
### shouldReattach(): Optional<Boolean>
Optional; if the message needs to be reattached