Adding span collection limits

[lalitb]

As per the recent spec change :

Max attributes per span : 1000
Max links per span : 1000
Max events per span : 1000

The upper bound needs to be validated.

[pyohannes]

Those limits are not mandatory by the spec (they're a MAY), so I will remove the bug label.

[lalitb]

@anshulkumar19 - I have assigned it to myself, while you are working on it ( to ensure there is no parallel work on it ).

[anshulkumar19]

Thanks @lalitb

[anshulkumar19]

@lalitb Currently this is WIP (span limit struct is added but constraint is used only in span_data ), intended to get it reviewed from the perspective of complexity introduced in current structure as this is an optional feature suggested by the spec.