RFR: 1701: Make use of Etag optional for MailingListArchiveReaderBot [v2]

[Erik Joelsson]

> We are experiencing long delays from when a user posts an email to a PR thread to when the MailingListArchiveReaderBot posts it as a comment to the PR. I think this is caused by the service provider for the mailinglists archive not handling Etags correctly. While that is sorted out, we need to be able to turn the use of etags off. This patch makes it a configuration parameter.

Erik Joelsson has updated the pull request incrementally with one additional commit since the last revision:

  Fix test

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Changes:
  - all: https://git.openjdk.org/skara/pull/1430/files
  - new: https://git.openjdk.org/skara/pull/1430/files/fe4f7b79..0ab638b9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1430&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1430&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1430.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1430/head:pull/1430

PR: https://git.openjdk.org/skara/pull/1430