[enrichments] Add exception based enrichment for span events

[lahsivjar]

Span events should be enriched with the following attributes:

• error.id (unique number for the given error instance)
• error.exception.message
• error.exception.stacktrace
• error.exception.cause
• error.exception.handled
• error.grouping_key

[AlexanderWert]

@lahsivjar FYI: added error.id to the above list!