feat: Add ObservationTimeSeries service and entity class

pom.xml

src/main/java/no/nibio/vips/logic/VIPSLogicApplication.java

.../nibio/vips/logic/controller/session/ObservationBean.java

...s/logic/controller/session/ObservationTimeSeriesBean.java

src/main/java/no/nibio/vips/logic/entity/Observation.java

...ava/no/nibio/vips/logic/entity/ObservationTimeSeries.java

.../java/no/nibio/vips/logic/service/ObservationService.java

...ibio/vips/logic/service/ObservationTimeSeriesService.java

src/main/java/no/nibio/vips/logic/service/POIService.java

.../vips/logic/service/ObservationTimeSeriesServiceTest.java