Restart LOB mining based on the oldest LOB-based transaction in cache, not oldest transaction in cache. [DBZ-7894]

Migrated from [DBZ-7894](https://issues.redhat.com/browse/DBZ-7894)

h2. Which use case/requirement will be addressed by the proposed feature?

In the method *MemoryLogMinerEventProcessor#calculateNewStartScn:

That LOB is enabled and the transaction cache is empty indicates that the last mining session did not capture any START event between the last startSCN and the last endSCN. So we can begin the next mining session from where we left off just like the way that the LOB is disabled rather than the maxCommittedScn. If we use the maxCommittedScn, the maxCommittedScn could _remain unchanged for a long period of time in the case of not capturing any event_ {_}for a long period of time, which increases the possibility of "{_}ORA-01291: _missing log file"._