Fixes 404 return code when calling tabletMergabilityInfo.

[ddanielr]

Saw the following Error message in console log that mentioned the Duration datatype was not able to be serialized.

Java 8 date/time type `java.time.Duration` not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable handling (through reference chain: java.util.Collections$SynchronizedRandomAccessList[1]->org.apache.accumulo.monitor.next.SystemInformation$SanitizedTabletInformation["tabletMergeabilityInfo"]->org.apache.accumulo.core.client.admin.TabletMergeabilityInfo["tabletMergeability"]->org.apache.accumulo.core.client.admin.TabletMergeability["delay"])

Added the jackson JavaTimeModule to fix the 404 return.
Tested locally and confirmed the 404 return code was fixed.