RFR: 8236: Add support for Jolokia discovery

[Martin Skarsaune]

Jolokia comes with a discovery mechanism. It is helpful to make use of this to automatically populate the JVM browser, alongside local JVM and other discovery mechanisms.

https://jolokia.org/reference/html/manual/jolokia_protocol.html#discovery

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Commit messages:
 - JMC-8236: Simplify string externalization and other cleanup.
 - JMC-8236: Add support for jolokia discovery

Changes: https://git.openjdk.org/jmc/pull/570/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=570&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8236
  Stats: 1042 lines in 21 files changed: 1017 ins; 7 del; 18 mod
  Patch: https://git.openjdk.org/jmc/pull/570.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/570/head:pull/570

PR: https://git.openjdk.org/jmc/pull/570