Support instant_time/commit_time of savepoint procedure optional

[hudi-bot]

Procedure parameter instant_time/commit_time of savepoint procedure optional could be optional and uses the latest instant when the value of instant_time/commit_time is null or empty.

JIRA info

• Link: https://issues.apache.org/jira/browse/HUDI-6218
• Type: Improvement
• Fix version(s):
  • 1.1.0