RFR: 8311000: missing @since info in jdk.management

[Kevin Walls]

Simple addition of a doc tag.  

src/share/classes/com/sun/management/GarbageCollectionNotificationInfo.java is introduced in jdk7 by
7036199: Adding a notification to the implementation of GarbageCollectorMXBeans

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Commit messages:
 - 8311000: missing @since info in jdk.management

Changes: https://git.openjdk.org/jdk/pull/14708/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14708&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311000
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14708.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14708/head:pull/14708

PR: https://git.openjdk.org/jdk/pull/14708