RFR: 1514: Add metrics for mailing list archive polling

Thu Jul 28 18:54:12 UTC 2022

This patch adds a new metrics counter tracking the polling rate for the MailmanListReader. I would like to get this live before trying to reduce the polling rate in SKARA-1513, so that any improvements can be accurately measured.

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Commit messages:
 - SKARA-1514

Changes: https://git.openjdk.org/skara/pull/1342/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1342&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1514
  Stats: 8 lines in 3 files changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1342.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1342/head:pull/1342

PR: https://git.openjdk.org/skara/pull/1342