text: Title: Add execution errors and statistics to JSON output generated by Rebot
  Body: We added support to generate JSON output files with Rebot in RF 7.0 (#4847) as mentioned in the [issue comment](https://github.com/robotframework/robotframework/issues/4847#issuecomment-1861733290), the generated output only contains information about the executed suite, not execution errors or statistics that normal XML outputs contain. Rebot itself doesn't need statistics if it is used for further processing JSON outputs (it always re-calculates them), but execution errors being omitted means that they aren't available in generated logs ether. That is a pretty severe limitation and needs to be fixed.
  
  The initial idea was to add errors and statistics to JSON outputs when adding support to generate JSON outputs already during execution (#3423). That is a pretty big task currently planned for RF 8.0 and  I believe we should fix the issue with errors and statistics already earlier.
  
  A problem with the change is that it is backwards incompatible and external tools processing JSON output files need to be updated. It could be argued that such a change should wait for a major release, but I believe this is important enough enhancement to be done sooner. Tools would need to be updated anyway, regardless the version number, and the more we wait the more there are tools to be updated.