Add streaming-related fields to DiagnoseOutput schema

[jthreefoot-edb]

Add SystemInfo to the additionalproperties of DiagnoseOutput.servers as a required field

Add to Status

• included_files (as we have under Backups)
• pg_receivexlog_compatible - bool
• pg_receivexlog_installed - bool
• pg_receivexlog_path - string
• pg_receivexlog_supports_slots - bool
• pg_receivexlog_synchronous - bool
• pg_receivexlog_version - string (the other version numbers in the schema are strings)
• postgres_systemid - string or number?
• streaming - bool
• streaming_supported - bool
• streaming_systemid - string or number?
• timeline - int?
• xlogpos - string
  I believe all of these should be nullable, as they aren't relevant to all barman/postgres setups.