Add yaml semantic conventions for Exception

[thisthat]

Changes

Updated Exception semantic convention to the YAML format.

Related issues #547

[carlosalberto]

@thisthat Please rebase and resolve the conflicts ;)

[thisthat]

@carlosalberto done in 22bbb9b :)

[tigrannajaryan]

Blocking just to understand clearly the intent regarding exception.stacktrace. The PR itself is highly welcome, but I think the way the example is rendered makes it confusing.

[Oberon00]

Indeed it seems like the \n are not doing what they should inside the ''.

[thisthat]

@tigrannajaryan could you please explain better the problem? Do you want the example to be encapsulated in quotes?
@Oberon00 also in the previous version the example had \n that were not rendered as new lines

[Oberon00]

@thisthat You are right: https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/exceptions.md#attributes

[tigrannajaryan]

I think the original example was also misleading. I expect not to see any literal \n characters in the example and I expect not to see backslaches before double quote characters.
It needs to be fixed, but I am fine if it is fixed in a future PR.

[thisthat]

@tigrannajaryan I've created #951 to track the example change