Adding an annotation with a space in the key silently fails

[scottgerring]

Per this issue over on powertools for Java: aws-powertools/powertools-lambda-java#1499
If a user adds a trace annotation with a space in it, the annotation is silently not added to the trace.

It looks like annotation keys have to be alphanumeric without spaces for X-Ray. It would be great if the X-Ray SDK could through a runtime exception or something, so we get some indication that the thing we are doing isn't going to work, rather than silently accepting bad data.

What do you think?