[🍒][CDAP-21093] Add ExternalDocumentationLink in abstract sink #1198

Job	Run time
build (mysql-plugin)	1h 16m 50s
build (postgresql-plugin)	32m 31s
build (oracle-plugin)	1h 47m 46s
build (mssql-plugin)	1h 20m 25s
build (cloudsql-mysql-plugin)	1h 18m 40s
build (cloudsql-postgresql-plugin)	7m 26s
	6h 23m 38s

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