[FLINK-31536] Support to set watermark emit strategy in sql layer

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.18.0
• Component/s: Table SQL / Runtime
• Assignee: Yuan Kui
• Reporter: Yuan Kui
• Created: 21/Mar/23 11:36
• Updated: 17/Jul/23 09:52
• Resolved: 17/Jul/23 09:52

Description

Support to configure the watermark emit strategy for the source which implements the `SupportsWatermarkPushDown` interface. 

User could configure the watermark emit strategy in flink sql job with table options or 'OPTIONS' hint，as discussed in  https://cwiki.apache.org/confluence/display/FLINK/FLIP-296%3A+Extend+watermark-related+features+for+SQL