Add options field on Label model for controlling advanced options.

Suggestion to add place holder for options per Label.

While I was using S2Graph in production, there were many cases to control whether publishing or not publishing input request to Kafka(WALLOG).

For more detail, let me share my case.
When I insert bulk data(or immutable data that is produced by batch processing, for example similarity matrix), I do not want to publish inserted Edge into WALLOG, since all data is duplicate from original bulk data.

Maybe options to control publishing all/sampling/drop WALLOG per each EDGE can be helpful.

Also the benefit of automatically(implicitly) create reverse direction index can be problematic in some case like S2GRAPH-123.

For example, user insert edge a->out->101, then 101<-in<-a also automatically created and some case, especially 101 has lots of incoming edges which means 101 is super-node, user may want to skip implicit reverse direction edge.

I think we have no idea what other options may be necessary, so I am suggesting add options field on Label to hold advanced options.

In my opinion, storing JSON string(kind like config) as options make sense since it is easy to implement, but I am open to any other suggestions.