fix: kafkaexporter:- log span tags when debug and dump_span_attributes are set

[tim-mwangi]

Description

Have the option to log the tag value's length or actual value depending on if dump_span_attributes is set. This is for the scenario where a span exceeds the producer maxMessageBytes. Follow up to https://github.com/hypertrace/hypertrace-collector/pull/69

Checklist:

• [✅ ] My changes generate no new warnings
• [✅ ] I have added tests that prove my fix is effective or that my feature works