Handling timezone in SemConv

[gregkalapos]

In #1116 we introduce geo fields to SemConv. One of the fields from the ECS geo fields (which the PR is based on) is geo.timezone. Discussion: #1116 (comment) and #1116 (comment).

Goal of this issue is:

• Discuss if timezone should be its own thing
• If so, what fields does it have and what format does SemConv expect? (enforcing some common timezone format vs. just a string)
• Decide the exact meaning of timezone. Is it dependent on daylights saving or not? If it is, is it the timezone when the event occurred vs. when the event is consumed?