DbLedgerStorage does not persist ExplicitLAC: Information (Header) of TransientLedgerInfo is not persisted

**FEATURE REQUEST**

1. Please describe the feature you are requesting.

TransientLedgerInfo class borrows the logic from FileInfo, which is used for holding all the transient states for a given ledger when DbLedgerStorage is used for LedgerStorage. But unlike FileInfo, in TransientLedgerInfo, Header (containing masterKey, stateBits and explicitLac) is not defined and it is not persisted.

2. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have). Are you currently using any workarounds to address this issue?

With https://github.com/apache/bookkeeper/issues/1527 we are going to persist explicitLac, but since TransientLedgerInfo doesn't has Header/persistence logic, for now I'm going to ignore persisting explicitLac logic in TransientLedgerInfo/DbLedgerStorage case.

Check Ignored test case here:
https://github.com/apache/bookkeeper/blob/master/bookkeeper-server/src/test/java/org/apache/bookkeeper/client/ExplicitLacTest.java#L145