chore: Rename dueDate to scheduledDate in service layer [TECH-1615]

[enricocolasante]

scheduledAt field in Event was internally translated to dueDate.
This PR aims to replace all occurrences of dueDate in the service layer to scheduledDate.
The general rule that we are using is that date fields are suffixed with At in the API and then suffixed with Date in the service and the DB layer.

Next PRs

• Rename occurredAt in DB layer
• Rename scheduledAt in DB layer

[muilpp]

the two failing tests are caused by still using the field dueDate

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

[codecov]

Codecov Report

Merging #15617 (1d430b0) into master (b6648ef) will decrease coverage by 0.01%.
The diff coverage is 78.78%.

@@             Coverage Diff              @@
##             master   #15617      +/-   ##
============================================
- Coverage     66.24%   66.23%   -0.01%     
+ Complexity    31262    31260       -2     
============================================
  Files          3485     3485              
  Lines        129788   129789       +1     
  Branches      15145    15145              
============================================
- Hits          85973    85972       -1     
  Misses        36731    36731              
- Partials       7084     7086       +2     

Flag	Coverage Δ
integration	49.80% <69.69%> (+<0.01%)	⬆️
integration-h2	32.41% <21.21%> (-0.01%)	⬇️
unit	30.34% <54.54%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...api/src/main/java/org/hisp/dhis/program/Event.java	95.60% <100.00%> (ø)
...ation/ProgramStageNotificationMessageRenderer.java	75.71% <100.00%> (ø)
...ava/org/hisp/dhis/program/DefaultEventService.java	27.17% <100.00%> (ø)
...sp/dhis/program/hibernate/HibernateEventStore.java	65.78% <ø> (ø)
...hisp/dhis/sms/listener/CompressionSMSListener.java	72.66% <100.00%> (ø)
.../dxf2/deprecated/tracker/event/JdbcEventStore.java	49.42% <100.00%> (ø)
...importer/context/ProgramStageInstanceSupplier.java	93.22% <100.00%> (ø)
...er/importer/mapper/ProgramStageInstanceMapper.java	92.77% <100.00%> (ø)
.../engine/DefaultProgramRuleEntityMapperService.java	79.09% <100.00%> (+0.05%)	⬆️
...dhis/tracker/export/event/DefaultEventService.java	95.45% <100.00%> (ø)
... and 12 more

... and 1 file with indirect coverage changes

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