Bigtable: investigate GCRule.fromProto being incorrect

[igorbernstein2]

From a user:

GCRule and GcRule classes are confusing and .fromProto() conversion does not work properly in some cases. Not 100% sure which scenario it was, but I think we were setting maxversions and maxage, and only one of them was in the final result after calling .fromProto().

[sduskis]

@igorbernstein2, and additional info would be helpful.

[igorbernstein2]

I updated the description

[sduskis]

@rahulKQL, can you please look at this?