Migrate python pages to java in java-sdk documentation

[manishbansal8843]

https://docs.couchbase.com/java-sdk/2.7/core-operations.html page has python code. Same needs to be migrated.

[RichardSmedley]

Thanks, waiting on https://issues.couchbase.com/browse/JCBC-1264
but appreciate #70
Will look at it after weekend 👍
(it's 8pm in this timezone)