feat(make_idempotent): support making incr request idempotent in pegasus_write_service::impl

[empiredan]

Implement two APIs making incr request idempotent in pegasus_write_service::impl:

• translate an incr request (non-idempotent) into a single-put request (idempotent),
  and process the possible errors during the translation, e.g. failed to read base value for
  increment from the RocksDB instance;
• apply the single-put request into the RocksDB instance and make response for incr.

[acelyc111]

When will expire_ts_seconds to be less than 0?

[empiredan]

Yes, -1 means clearing TTL as is described by Java client if ttlSeconds == -1, then update to no ttl if increment succeed. (see https://github.com/apache/incubator-pegasus/blob/master/java-client/src/main/java/org/apache/pegasus/client/PegasusClientInterface.java#L561); and Java client would throw exception once it is less than -1 (see https://github.com/apache/incubator-pegasus/blob/master/java-client/src/main/java/org/apache/pegasus/client/PegasusTable.java#L733).
On server-side, currently non-idempotent incr would also clear TTL once it is less than 0 (see https://github.com/apache/incubator-pegasus/blob/master/src/server/pegasus_write_service_impl.h#L235).