ReportNode V2.1

[flo-dup]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? No

What kind of change does this PR introduce? Feature / bug fix

What is the current behavior?

• ReportNode v2.0
• context of included ReportNode is not replaced by context of new root ReportNode
• included ReportNode is silently replacing messageTemplate if key conflicts occur
• Deserialization loads the whole file before deserializing it
• No timestamps (except if added manually)
• messageTemplate needed to construct ReportNodes

What is the new behavior (if this is a feature change)?

• ReportNode v2.1
• context of included ReportNode is replaced by context of new root ReportNode through RefChain
• if messageTemplate key conflicts occur when including ReportNode, templates are not overridden, + warn log
• Deserializes the JSON reportNode file while streaming it
• Timestamp value added for each ReportNode with a specific pattern if enabled at root ReportNode creation
• messageTemplate can be missing at ReportNode construction (to anticipate the dictionaries questions which will later arise)

Does this PR introduce a breaking change or deprecate an API?

• [x] Yes
• [ ] No

If yes, please check if the following requirements are fulfilled

• [x] The Breaking Change or Deprecated label has been added
• [x] The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

• Starting from this release, the reportNode JSON files from API v2.0 cannot be read anymore. Please switch to JSON files generated with API V2.1.
• ReportConstants.REPORT_SEVERITY_KEY has been renamed into ReportConstants.SEVERITY_KEY