[FLINK-36938] Provide hooks before and after the watermark processing #299

Job	Run time
Pre-compile Checks / Basic QA	8m 9s
Default (Java 11) / Compile	18m 36s
Default (Java 11) / E2E (group 1)	1h 47m 10s
Default (Java 11) / Test (module: core)	29m 10s
Default (Java 11) / E2E (group 2)	2h 3m 12s
Default (Java 11) / Test packaging/licensing	34m 3s
Default (Java 11) / Test (module: python)	29m 53s
Default (Java 11) / Test (module: table)	31m 50s
Default (Java 11) / Test (module: connect)	6m 52s
Default (Java 11) / Test (module: tests)	36m 30s
Default (Java 11) / Test (module: misc)	27m 22s
	7h 32m 47s

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