Fix: add Transactional annotation to method to fix "no session" error

[pieterlukasse]

Link to JIRA ticket if there is one: https://ctds-planx.atlassian.net/browse/VADC-1319

Bug Fixes

• fixes the error

2024-08-29 15:03:15.050 ERROR http-nio-8080-exec-16 org.ohdsi.webapi.util.GenericExceptionMapper - [] - 
org.springframework.core.convert.ConversionFailedException: Failed to convert from type 
[org.ohdsi.webapi.feanalysis.domain.FeAnalysisWithPrevalenceCriteriaEntity] to type 
[org.ohdsi.webapi.feanalysis.dto.FeAnalysisDTO] for value 
'org.ohdsi.webapi.feanalysis.domain.FeAnalysisWithPrevalenceCriteriaEntity@8b'; nested exception is 
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: 
org.ohdsi.webapi.feanalysis.domain.FeAnalysisWithCriteriaEntity.design, could not initialize proxy - no Session

...
at...
 org.ohdsi.webapi.feanalysis.converter.FeAnalysisEntityToFeAnalysisDTOConverter.convertDesignToJson(FeAnalysisEntityToFeAnalysisDTOConverter.java:53)
	at org.ohdsi.webapi.feanalysis.converter.FeAnalysisEntityToFeAnalysisDTOConverter.convert(FeAnalysisEntityToFeAnalysisDTOConverter.java:26)
	at org.ohdsi.webapi.feanalysis.converter.FeAnalysisEntityToFeAnalysisDTOConverter.convert(FeAnalysisEntityToFeAnalysisDTOConverter.java:17)