[DL-12022] Clarified the description of the netVatDue field

[abutters]

Clarified the description of the netVatDue field in the API documentation for the Submit VAT return for period endpoint.

[platops-pr-bot]

• SBT can be updated to 1.7.2 in project/build.properties
• uk.gov.hmrc.sbt-auto-build can be updated to 3.14.0 in project/plugins.sbt
• uk.gov.hmrc.sbt-distributables can be updated to 2.2.0 in project/plugins.sbt
• Config key auditing.traceRequests can be removed from conf/application.conf. It has been unused since play-auditing:3.0.0
• System property lookup can be removed in conf/application-json-logger.xml - Bootstrap's LoggerModule allows configuration of loggers without this - See confluence https://confluence.tools.tax.service.gov.uk/x/9oH1FQ
• Config key play.http.secret.key can be removed from conf/application.conf. This is already provided by Bootstrap
• Deprecated config uk.gov.hmrc.play.bootstrap.AuditModule can be changed to uk.gov.hmrc.play.audit.AuditModule in conf/application.conf
• Add uk.gov.hmrc.bootstrap-test-play-28 in project/AppDependencies.scala to provide recommended test dependencies. Use a variable to keep version in sync with bootstrap-play