Use digest for dup check instead of raw record

[daigotanaka]

tap-rest-api keeps a copy of the last extracted record in the bookmark (aka state) together with the last recorded index or timestamp. The extra information is used to ignore the same record in the next run with the bookmark whose start index/time is inclusive.

However, It is not a good practice to include a raw record in the bookmark items mainly for security reasons.

So we should

1. Sort the last record (except the extraction time key), by keys
2. create a md5 digest
3. include the digest instead of raw record in the bookmark.

To ensure backward compatibility, the dup check is made for both raw record and the digest.

[daigotanaka]

This will also resolve some of the target incompatible issues related to JSON serialization:

e.g. target-snowflake:

TypeError: Object of type 'Decimal' is not JSON serializable