DL-10396 - added message field to documentation

[platops-pr-bot]

• SBT can be updated to 1.7.2 in project/build.properties
• Scala can be updated from 2.12.15 to 2.13.8 in build.sbt
• uk.gov.hmrc.sbt-auto-build can be updated to 3.9.0 in project/plugins.sbt
• uk.gov.hmrc.sbt-distributables can be updated to 2.2.0 in project/plugins.sbt
• System property lookup can be removed in conf/application-json-logger.xml - Bootstrap's LoggerModule allows configuration of loggers without this. See README https://github.com/hmrc/bootstrap-play#version-5180
• 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